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 $58.98   10.193%   $64.9918   $64.99   $65.00   $65.00  
  Purchase #2 $188.63   4.552%   $197.2164   $197.22   $197.20   $197.20  
  Purchase #3 $54.56   13.838%   $62.11   $62.11   $62.10   $62.10  
  Purchase #4 $143.28   11.138%   $159.2385   $159.24   $159.25   $159.20  
  Purchase #5 $124.87   8.335%   $135.2779   $135.28   $135.30   $135.30  
  Purchase #6 $52.54   13.305%   $59.5304   $59.53   $59.55   $59.50  
  Purchase #7 $250.92   6.824%   $268.0428   $268.04   $268.05   $268.00  
  7 purchase totals = $873.78       $946.4078   $946.41   $946.45   $946.30