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 $60.43   9.126%   $65.9448   $65.94   $65.95   $65.90  
  Purchase #2 $185.88   10.467%   $205.3361   $205.34   $205.35   $205.30  
  Purchase #3 $203.45   3.431%   $210.4304   $210.43   $210.45   $210.40  
  Purchase #4 $51.27   9.205%   $55.9894   $55.99   $56.00   $56.00  
  Purchase #5 $115.92   8.672%   $125.9726   $125.97   $125.95   $126.00  
  Purchase #6 $245.67   13.498%   $278.8305   $278.83   $278.85   $278.80  
  Purchase #7 $13.86   10.188%   $15.2721   $15.27   $15.25   $15.30  
  7 purchase totals = $876.48       $957.7759   $957.77   $957.80   $957.70