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 $56.89   8.291%   $61.6067   $61.61   $61.60   $61.60  
  Purchase #2 $240.80   6.831%   $257.249   $257.25   $257.25   $257.20  
  Purchase #3 $185.31   5.741%   $195.9486   $195.95   $195.95   $195.90  
  Purchase #4 $84.98   7.303%   $91.1861   $91.19   $91.20   $91.20  
  Purchase #5 $148.98   4.226%   $155.2759   $155.28   $155.30   $155.30  
  Purchase #6 $60.81   6.800%   $64.9451   $64.95   $64.95   $64.90  
  Purchase #7 $125.37   3.495%   $129.7517   $129.75   $129.75   $129.80  
  7 purchase totals = $903.14       $955.9631   $955.98   $956.00   $955.90