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 $38.29   8.242%   $41.4459   $41.45   $41.45   $41.40  
  Purchase #2 $189.27   8.300%   $204.9794   $204.98   $205.00   $205.00  
  Purchase #3 $189.53   8.125%   $204.9293   $204.93   $204.95   $204.90  
  Purchase #4 $49.39   7.482%   $53.0854   $53.09   $53.10   $53.10  
  Purchase #5 $38.62   9.754%   $42.387   $42.39   $42.40   $42.40  
  Purchase #6 $6.38   12.214%   $7.1593   $7.16   $7.15   $7.20  
  Purchase #7 $157.63   13.661%   $179.1638   $179.16   $179.15   $179.20  
  7 purchase totals = $669.11       $733.1501   $733.16   $733.20   $733.20