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 $228.98   13.811%   $260.6044   $260.60   $260.60   $260.60  
  Purchase #2 $25.56   6.656%   $27.2613   $27.26   $27.25   $27.30  
  Purchase #3 $57.95   11.164%   $64.4195   $64.42   $64.40   $64.40  
  Purchase #4 $69.97   9.671%   $76.7368   $76.74   $76.75   $76.70  
  Purchase #5 $237.57   5.625%   $250.9333   $250.93   $250.95   $250.90  
  Purchase #6 $52.72   8.384%   $57.14   $57.14   $57.15   $57.10  
  Purchase #7 $185.42   5.609%   $195.8202   $195.82   $195.80   $195.80  
  7 purchase totals = $858.17       $932.9155   $932.91   $932.90   $932.80