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 $182.36   12.241%   $204.6827   $204.68   $204.70   $204.70  
  Purchase #2 $235.70   6.319%   $250.5939   $250.59   $250.60   $250.60  
  Purchase #3 $104.58   11.648%   $116.7615   $116.76   $116.75   $116.80  
  Purchase #4 $129.83   13.138%   $146.8871   $146.89   $146.90   $146.90  
  Purchase #5 $56.86   3.350%   $58.7648   $58.76   $58.75   $58.80  
  Purchase #6 $249.63   5.757%   $264.0012   $264.00   $264.00   $264.00  
  Purchase #7 $207.92   13.652%   $236.3052   $236.31   $236.30   $236.30  
  7 purchase totals = $1,166.88       $1,277.9964   $1,277.99   $1,278.00   $1,278.10