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 $227.96   9.733%   $250.1473   $250.15   $250.15   $250.10  
  Purchase #2 $44.41   8.557%   $48.2102   $48.21   $48.20   $48.20  
  Purchase #3 $119.36   10.817%   $132.2712   $132.27   $132.25   $132.30  
  Purchase #4 $215.68   5.222%   $226.9428   $226.94   $226.95   $226.90  
  Purchase #5 $73.79   6.521%   $78.6018   $78.60   $78.60   $78.60  
  Purchase #6 $205.25   7.857%   $221.3765   $221.38   $221.40   $221.40  
  Purchase #7 $50.38   11.665%   $56.2568   $56.26   $56.25   $56.30  
  7 purchase totals = $936.83       $1,013.8066   $1,013.81   $1,013.80   $1,013.80