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 $113.88   13.576%   $129.3403   $129.34   $129.35   $129.30  
  Purchase #2 $223.39   9.197%   $243.9352   $243.94   $243.95   $243.90  
  Purchase #3 $250.63   4.502%   $261.9134   $261.91   $261.90   $261.90  
  Purchase #4 $178.28   8.188%   $192.8776   $192.88   $192.90   $192.90  
  Purchase #5 $75.90   8.133%   $82.0729   $82.07   $82.05   $82.10  
  Purchase #6 $201.77   12.622%   $227.2374   $227.24   $227.25   $227.20  
  Purchase #7 $183.39   6.726%   $195.7248   $195.72   $195.70   $195.70  
  7 purchase totals = $1,227.24       $1,333.1016   $1,333.10   $1,333.10   $1,333.00