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 $168.44   9.659%   $184.7096   $184.71   $184.70   $184.70  
  Purchase #2 $54.71   4.287%   $57.0554   $57.06   $57.05   $57.10  
  Purchase #3 $195.54   7.643%   $210.4851   $210.49   $210.50   $210.50  
  Purchase #4 $93.47   6.294%   $99.353   $99.35   $99.35   $99.40  
  Purchase #5 $8.66   3.715%   $8.9817   $8.98   $9.00   $9.00  
  Purchase #6 $247.61   11.797%   $276.8206   $276.82   $276.80   $276.80  
  Purchase #7 $219.50   4.389%   $229.1339   $229.13   $229.15   $229.10  
  7 purchase totals = $987.93       $1,066.5393   $1,066.54   $1,066.55   $1,066.60