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 $247.85   10.258%   $273.2745   $273.27   $273.25   $273.30  
  Purchase #2 $92.87   12.770%   $104.7295   $104.73   $104.75   $104.70  
  Purchase #3 $170.27   8.158%   $184.1606   $184.16   $184.15   $184.20  
  Purchase #4 $41.68   10.105%   $45.8918   $45.89   $45.90   $45.90  
  Purchase #5 $116.69   13.478%   $132.4175   $132.42   $132.40   $132.40  
  Purchase #6 $228.57   7.536%   $245.795   $245.80   $245.80   $245.80  
  Purchase #7 $33.62   13.634%   $38.2038   $38.20   $38.20   $38.20  
  7 purchase totals = $931.55       $1,024.4727   $1,024.47   $1,024.45   $1,024.50