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 $175.74   12.480%   $197.6724   $197.67   $197.65   $197.70  
  Purchase #2 $244.95   6.818%   $261.6507   $261.65   $261.65   $261.70  
  Purchase #3 $229.44   3.773%   $238.0968   $238.10   $238.10   $238.10  
  Purchase #4 $182.73   12.589%   $205.7339   $205.73   $205.75   $205.70  
  Purchase #5 $211.31   4.121%   $220.0181   $220.02   $220.00   $220.00  
  Purchase #6 $139.54   4.778%   $146.2072   $146.21   $146.20   $146.20  
  Purchase #7 $207.90   8.778%   $226.1495   $226.15   $226.15   $226.10  
  7 purchase totals = $1,391.61       $1,495.5286   $1,495.53   $1,495.50   $1,495.50