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 $116.53   8.781%   $126.7625   $126.76   $126.75   $126.80  
  Purchase #2 $91.36   5.848%   $96.7027   $96.70   $96.70   $96.70  
  Purchase #3 $209.82   3.788%   $217.768   $217.77   $217.75   $217.80  
  Purchase #4 $24.39   12.235%   $27.3741   $27.37   $27.35   $27.40  
  Purchase #5 $248.31   4.346%   $259.1016   $259.10   $259.10   $259.10  
  Purchase #6 $14.73   10.809%   $16.3222   $16.32   $16.30   $16.30  
  Purchase #7 $197.96   7.725%   $213.2524   $213.25   $213.25   $213.30  
  7 purchase totals = $903.10       $957.2835   $957.27   $957.20   $957.40