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 $66.61   11.584%   $74.3261   $74.33   $74.35   $74.30  
  Purchase #2 $124.81   6.103%   $132.4272   $132.43   $132.45   $132.40  
  Purchase #3 $196.91   6.261%   $209.2385   $209.24   $209.25   $209.20  
  Purchase #4 $55.79   13.497%   $63.32   $63.32   $63.30   $63.30  
  Purchase #5 $194.53   5.508%   $205.2447   $205.24   $205.25   $205.20  
  Purchase #6 $182.60   13.716%   $207.6454   $207.65   $207.65   $207.60  
  Purchase #7 $143.57   7.550%   $154.4095   $154.41   $154.40   $154.40  
  7 purchase totals = $964.82       $1,046.6114   $1,046.62   $1,046.65   $1,046.40