Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $183.29   10.629%   $202.7719   $202.77   $202.75   $202.80  
  Purchase #2 $239.39   6.667%   $255.3501   $255.35   $255.35   $255.40  
  Purchase #3 $133.59   8.261%   $144.6259   $144.63   $144.65   $144.60  
  Purchase #4 $210.59   11.705%   $235.2396   $235.24   $235.25   $235.20  
  Purchase #5 $248.47   11.754%   $277.6752   $277.68   $277.70   $277.70  
  Purchase #6 $246.82   12.425%   $277.4874   $277.49   $277.50   $277.50  
  Purchase #7 $194.85   3.163%   $201.0131   $201.01   $201.00   $201.00  
  7 purchase totals = $1,457.00       $1,594.1632   $1,594.17   $1,594.20   $1,594.20