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 $183.98   11.226%   $204.6336   $204.63   $204.65   $204.60  
  Purchase #2 $242.56   8.290%   $262.6682   $262.67   $262.65   $262.70  
  Purchase #3 $32.51   10.439%   $35.9037   $35.90   $35.90   $35.90  
  Purchase #4 $229.42   13.716%   $260.8872   $260.89   $260.90   $260.90  
  Purchase #5 $225.83   8.289%   $244.549   $244.55   $244.55   $244.50  
  Purchase #6 $243.93   4.686%   $255.3606   $255.36   $255.35   $255.40  
  Purchase #7 $94.99   5.239%   $99.9665   $99.97   $99.95   $100.00  
  7 purchase totals = $1,253.22       $1,363.9688   $1,363.97   $1,363.95   $1,364.00