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 $191.59   6.660%   $204.3499   $204.35   $204.35   $204.30  
  Purchase #2 $237.79   7.362%   $255.2961   $255.30   $255.30   $255.30  
  Purchase #3 $44.33   8.478%   $48.0883   $48.09   $48.10   $48.10  
  Purchase #4 $16.50   3.473%   $17.073   $17.07   $17.05   $17.10  
  Purchase #5 $77.75   12.472%   $87.447   $87.45   $87.45   $87.40  
  Purchase #6 $154.65   4.486%   $161.5876   $161.59   $161.60   $161.60  
  Purchase #7 $165.87   11.752%   $185.363   $185.36   $185.35   $185.40  
  7 purchase totals = $888.48       $959.2049   $959.21   $959.20   $959.20