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 $62.71   9.113%   $68.4248   $68.42   $68.40   $68.40  
  Purchase #2 $129.44   9.612%   $141.8818   $141.88   $141.90   $141.90  
  Purchase #3 $66.74   4.785%   $69.9335   $69.93   $69.95   $69.90  
  Purchase #4 $165.50   10.167%   $182.3264   $182.33   $182.35   $182.30  
  Purchase #5 $44.47   9.349%   $48.6275   $48.63   $48.65   $48.60  
  Purchase #6 $248.96   6.296%   $264.6345   $264.63   $264.65   $264.60  
  Purchase #7 $200.46   8.348%   $217.1944   $217.19   $217.20   $217.20  
  7 purchase totals = $918.28       $993.0229   $993.01   $993.10   $992.90