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 $48.83   6.823%   $52.1617   $52.16   $52.15   $52.20  
  Purchase #2 $92.46   12.352%   $103.8807   $103.88   $103.90   $103.90  
  Purchase #3 $84.25   10.689%   $93.2555   $93.26   $93.25   $93.30  
  Purchase #4 $105.33   8.347%   $114.1219   $114.12   $114.10   $114.10  
  Purchase #5 $248.57   5.126%   $261.3117   $261.31   $261.30   $261.30  
  Purchase #6 $205.38   13.128%   $232.3423   $232.34   $232.35   $232.30  
  Purchase #7 $74.71   11.631%   $83.3995   $83.40   $83.40   $83.40  
  7 purchase totals = $859.53       $940.4733   $940.47   $940.45   $940.50