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 $59.77   13.859%   $68.0535   $68.05   $68.05   $68.10  
  Purchase #2 $207.59   9.792%   $227.9172   $227.92   $227.90   $227.90  
  Purchase #3 $91.66   3.226%   $94.617   $94.62   $94.60   $94.60  
  Purchase #4 $195.30   11.569%   $217.8943   $217.89   $217.90   $217.90  
  Purchase #5 $107.29   5.370%   $113.0515   $113.05   $113.05   $113.10  
  Purchase #6 $150.31   9.519%   $164.618   $164.62   $164.60   $164.60  
  Purchase #7 $100.49   6.104%   $106.6239   $106.62   $106.60   $106.60  
  7 purchase totals = $912.41       $992.7754   $992.77   $992.70   $992.80