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 $246.26   6.121%   $261.3336   $261.33   $261.35   $261.30  
  Purchase #2 $172.30   11.105%   $191.4339   $191.43   $191.45   $191.40  
  Purchase #3 $214.60   7.466%   $230.622   $230.62   $230.60   $230.60  
  Purchase #4 $245.66   10.275%   $270.9016   $270.90   $270.90   $270.90  
  Purchase #5 $13.62   3.864%   $14.1463   $14.15   $14.15   $14.10  
  Purchase #6 $197.72   6.645%   $210.8585   $210.86   $210.85   $210.90  
  Purchase #7 $164.98   12.115%   $184.9673   $184.97   $184.95   $185.00  
  7 purchase totals = $1,255.14       $1,364.2632   $1,364.26   $1,364.25   $1,364.20