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 $241.81   9.561%   $264.9295   $264.93   $264.95   $264.90  
  Purchase #2 $213.90   9.334%   $233.8654   $233.87   $233.85   $233.90  
  Purchase #3 $190.32   9.664%   $208.7125   $208.71   $208.70   $208.70  
  Purchase #4 $164.53   12.258%   $184.6981   $184.70   $184.70   $184.70  
  Purchase #5 $79.91   5.343%   $84.1796   $84.18   $84.20   $84.20  
  Purchase #6 $27.74   12.728%   $31.2707   $31.27   $31.25   $31.30  
  Purchase #7 $24.98   3.194%   $25.7779   $25.78   $25.80   $25.80  
  7 purchase totals = $943.19       $1,033.4337   $1,033.44   $1,033.45   $1,033.50