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 $231.75   10.333%   $255.6967   $255.70   $255.70   $255.70  
  Purchase #2 $119.58   4.287%   $124.7064   $124.71   $124.70   $124.70  
  Purchase #3 $143.98   6.589%   $153.4668   $153.47   $153.45   $153.50  
  Purchase #4 $242.57   13.193%   $274.5723   $274.57   $274.55   $274.60  
  Purchase #5 $40.65   12.344%   $45.6678   $45.67   $45.65   $45.70  
  Purchase #6 $213.69   12.402%   $240.1918   $240.19   $240.20   $240.20  
  Purchase #7 $223.74   4.247%   $233.2422   $233.24   $233.25   $233.20  
  7 purchase totals = $1,215.96       $1,327.5440   $1,327.55   $1,327.50   $1,327.60