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 $249.43   8.185%   $269.8458   $269.85   $269.85   $269.80  
  Purchase #2 $154.90   10.504%   $171.1707   $171.17   $171.15   $171.20  
  Purchase #3 $65.38   3.259%   $67.5107   $67.51   $67.50   $67.50  
  Purchase #4 $12.38   6.867%   $13.2301   $13.23   $13.25   $13.20  
  Purchase #5 $243.95   7.385%   $261.9657   $261.97   $261.95   $262.00  
  Purchase #6 $119.88   10.191%   $132.097   $132.10   $132.10   $132.10  
  Purchase #7 $176.47   11.791%   $197.2776   $197.28   $197.30   $197.30  
  7 purchase totals = $1,022.39       $1,113.0976   $1,113.11   $1,113.10   $1,113.10