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 $43.39   7.383%   $46.5935   $46.59   $46.60   $46.60  
  Purchase #2 $240.69   6.759%   $256.9582   $256.96   $256.95   $257.00  
  Purchase #3 $104.39   9.633%   $114.4459   $114.45   $114.45   $114.40  
  Purchase #4 $138.45   12.189%   $155.3257   $155.33   $155.35   $155.30  
  Purchase #5 $215.30   10.329%   $237.5383   $237.54   $237.55   $237.50  
  Purchase #6 $245.88   11.491%   $274.1341   $274.13   $274.15   $274.10  
  Purchase #7 $189.49   10.454%   $209.2993   $209.30   $209.30   $209.30  
  7 purchase totals = $1,177.59       $1,294.2950   $1,294.30   $1,294.35   $1,294.20