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 $87.50   8.274%   $94.7398   $94.74   $94.75   $94.70  
  Purchase #2 $18.28   4.532%   $19.1084   $19.11   $19.10   $19.10  
  Purchase #3 $222.41   10.778%   $246.3813   $246.38   $246.40   $246.40  
  Purchase #4 $141.82   9.632%   $155.4801   $155.48   $155.50   $155.50  
  Purchase #5 $32.44   13.243%   $36.736   $36.74   $36.75   $36.70  
  Purchase #6 $240.46   6.872%   $256.9844   $256.98   $257.00   $257.00  
  Purchase #7 $90.66   6.317%   $96.387   $96.39   $96.40   $96.40  
  7 purchase totals = $833.57       $905.8170   $905.82   $905.90   $905.80