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 $24.64   4.552%   $25.7616   $25.76   $25.75   $25.80  
  Purchase #2 $140.61   13.694%   $159.8651   $159.87   $159.85   $159.90  
  Purchase #3 $84.73   8.296%   $91.7592   $91.76   $91.75   $91.80  
  Purchase #4 $35.62   4.514%   $37.2279   $37.23   $37.25   $37.20  
  Purchase #5 $236.38   12.767%   $266.5586   $266.56   $266.55   $266.60  
  Purchase #6 $228.29   4.471%   $238.4968   $238.50   $238.50   $238.50  
  Purchase #7 $241.94   5.259%   $254.6636   $254.66   $254.65   $254.70  
  7 purchase totals = $992.21       $1,074.3328   $1,074.34   $1,074.30   $1,074.50