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 $70.94   8.169%   $76.7351   $76.74   $76.75   $76.70  
  Purchase #2 $82.93   13.318%   $93.9746   $93.97   $93.95   $94.00  
  Purchase #3 $11.48   6.870%   $12.2687   $12.27   $12.25   $12.30  
  Purchase #4 $57.65   4.829%   $60.4339   $60.43   $60.45   $60.40  
  Purchase #5 $197.96   13.646%   $224.9736   $224.97   $224.95   $225.00  
  Purchase #6 $59.78   11.782%   $66.8233   $66.82   $66.80   $66.80  
  Purchase #7 $46.28   8.681%   $50.2976   $50.30   $50.30   $50.30  
  7 purchase totals = $527.02       $585.5068   $585.50   $585.45   $585.50