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 $194.49   4.819%   $203.8625   $203.86   $203.85   $203.90  
  Purchase #2 $156.93   9.373%   $171.639   $171.64   $171.65   $171.60  
  Purchase #3 $100.59   3.618%   $104.2293   $104.23   $104.25   $104.20  
  Purchase #4 $41.79   11.326%   $46.5231   $46.52   $46.50   $46.50  
  Purchase #5 $126.86   5.375%   $133.6787   $133.68   $133.70   $133.70  
  Purchase #6 $187.96   11.485%   $209.5472   $209.55   $209.55   $209.50  
  Purchase #7 $6.96   8.866%   $7.5771   $7.58   $7.60   $7.60  
  7 purchase totals = $815.58       $877.0569   $877.06   $877.10   $877.00