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 $250.54   6.823%   $267.6343   $267.63   $267.65   $267.60  
  Purchase #2 $12.55   12.863%   $14.1643   $14.16   $14.15   $14.20  
  Purchase #3 $202.32   3.784%   $209.9758   $209.98   $210.00   $210.00  
  Purchase #4 $79.41   11.425%   $88.4826   $88.48   $88.50   $88.50  
  Purchase #5 $190.65   11.478%   $212.5328   $212.53   $212.55   $212.50  
  Purchase #6 $99.34   3.108%   $102.4275   $102.43   $102.45   $102.40  
  Purchase #7 $53.71   11.264%   $59.7599   $59.76   $59.75   $59.80  
  7 purchase totals = $888.52       $954.9772   $954.97   $955.05   $955.00