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 $243.95   10.669%   $269.977   $269.98   $270.00   $270.00  
  Purchase #2 $205.62   10.766%   $227.757   $227.76   $227.75   $227.80  
  Purchase #3 $158.51   9.397%   $173.4052   $173.41   $173.40   $173.40  
  Purchase #4 $69.67   7.707%   $75.0395   $75.04   $75.05   $75.00  
  Purchase #5 $235.67   8.820%   $256.4561   $256.46   $256.45   $256.50  
  Purchase #6 $231.48   13.348%   $262.378   $262.38   $262.40   $262.40  
  Purchase #7 $225.29   5.781%   $238.314   $238.31   $238.30   $238.30  
  7 purchase totals = $1,370.19       $1,503.3268   $1,503.34   $1,503.35   $1,503.40