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 $178.97   8.770%   $194.6657   $194.67   $194.65   $194.70  
  Purchase #2 $250.81   4.235%   $261.4318   $261.43   $261.45   $261.40  
  Purchase #3 $46.37   5.254%   $48.8063   $48.81   $48.80   $48.80  
  Purchase #4 $88.73   3.826%   $92.1248   $92.12   $92.10   $92.10  
  Purchase #5 $71.68   5.731%   $75.788   $75.79   $75.80   $75.80  
  Purchase #6 $11.26   9.562%   $12.3367   $12.34   $12.35   $12.30  
  Purchase #7 $207.25   9.716%   $227.3864   $227.39   $227.40   $227.40  
  7 purchase totals = $855.07       $912.5397   $912.55   $912.55   $912.50