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 $249.93   4.446%   $261.0419   $261.04   $261.05   $261.00  
  Purchase #2 $43.54   9.158%   $47.5274   $47.53   $47.55   $47.50  
  Purchase #3 $43.93   5.154%   $46.1942   $46.19   $46.20   $46.20  
  Purchase #4 $139.85   6.843%   $149.4199   $149.42   $149.40   $149.40  
  Purchase #5 $122.35   6.690%   $130.5352   $130.54   $130.55   $130.50  
  Purchase #6 $182.59   9.864%   $200.6007   $200.60   $200.60   $200.60  
  Purchase #7 $207.31   11.416%   $230.9765   $230.98   $231.00   $231.00  
  7 purchase totals = $989.50       $1,066.2958   $1,066.30   $1,066.35   $1,066.20