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 $242.83   5.173%   $255.3916   $255.39   $255.40   $255.40  
  Purchase #2 $207.96   9.409%   $227.527   $227.53   $227.55   $227.50  
  Purchase #3 $110.94   7.525%   $119.2882   $119.29   $119.30   $119.30  
  Purchase #4 $191.46   11.754%   $213.9642   $213.96   $213.95   $214.00  
  Purchase #5 $131.75   13.777%   $149.9012   $149.90   $149.90   $149.90  
  Purchase #6 $217.28   4.469%   $226.9902   $226.99   $227.00   $227.00  
  Purchase #7 $244.60   9.505%   $267.8492   $267.85   $267.85   $267.80  
  7 purchase totals = $1,346.82       $1,460.9116   $1,460.91   $1,460.95   $1,460.90