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 $63.78   8.722%   $69.3429   $69.34   $69.35   $69.30  
  Purchase #2 $238.38   9.480%   $260.9784   $260.98   $261.00   $261.00  
  Purchase #3 $107.43   11.130%   $119.387   $119.39   $119.40   $119.40  
  Purchase #4 $58.99   6.794%   $62.9978   $63.00   $63.00   $63.00  
  Purchase #5 $41.74   6.647%   $44.5145   $44.51   $44.50   $44.50  
  Purchase #6 $30.36   3.733%   $31.4933   $31.49   $31.50   $31.50  
  Purchase #7 $103.42   11.507%   $115.3205   $115.32   $115.30   $115.30  
  7 purchase totals = $644.10       $704.0344   $704.03   $704.05   $704.00