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 $242.25   10.641%   $268.0278   $268.03   $268.05   $268.00  
  Purchase #2 $100.71   11.411%   $112.202   $112.20   $112.20   $112.20  
  Purchase #3 $30.76   13.316%   $34.856   $34.86   $34.85   $34.90  
  Purchase #4 $114.40   9.495%   $125.2623   $125.26   $125.25   $125.30  
  Purchase #5 $204.49   4.631%   $213.9599   $213.96   $213.95   $214.00  
  Purchase #6 $206.68   3.263%   $213.424   $213.42   $213.40   $213.40  
  Purchase #7 $141.80   3.387%   $146.6028   $146.60   $146.60   $146.60  
  7 purchase totals = $1,041.09       $1,114.3348   $1,114.33   $1,114.30   $1,114.40