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 $149.39   6.612%   $159.2677   $159.27   $159.25   $159.30  
  Purchase #2 $63.30   12.791%   $71.3967   $71.40   $71.40   $71.40  
  Purchase #3 $249.83   4.644%   $261.4321   $261.43   $261.45   $261.40  
  Purchase #4 $215.63   13.404%   $244.533   $244.53   $244.55   $244.50  
  Purchase #5 $154.94   4.703%   $162.2268   $162.23   $162.25   $162.20  
  Purchase #6 $158.58   4.806%   $166.2014   $166.20   $166.20   $166.20  
  Purchase #7 $84.94   13.507%   $96.4128   $96.41   $96.40   $96.40  
  7 purchase totals = $1,076.61       $1,161.4705   $1,161.47   $1,161.50   $1,161.40