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 $232.85   12.459%   $261.8608   $261.86   $261.85   $261.90  
  Purchase #2 $246.56   3.414%   $254.9776   $254.98   $255.00   $255.00  
  Purchase #3 $16.47   6.826%   $17.5942   $17.59   $17.60   $17.60  
  Purchase #4 $51.55   3.549%   $53.3795   $53.38   $53.40   $53.40  
  Purchase #5 $194.33   9.735%   $213.248   $213.25   $213.25   $213.20  
  Purchase #6 $31.98   13.570%   $36.3197   $36.32   $36.30   $36.30  
  Purchase #7 $182.46   9.169%   $199.1898   $199.19   $199.20   $199.20  
  7 purchase totals = $956.20       $1,036.5696   $1,036.57   $1,036.60   $1,036.60