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 $25.51   4.781%   $26.7296   $26.73   $26.75   $26.70  
  Purchase #2 $125.37   12.333%   $140.8319   $140.83   $140.85   $140.80  
  Purchase #3 $164.40   11.371%   $183.0939   $183.09   $183.10   $183.10  
  Purchase #4 $13.32   10.556%   $14.7261   $14.73   $14.75   $14.70  
  Purchase #5 $232.64   6.246%   $247.1707   $247.17   $247.15   $247.20  
  Purchase #6 $64.85   12.154%   $72.7319   $72.73   $72.75   $72.70  
  Purchase #7 $41.55   6.386%   $44.2034   $44.20   $44.20   $44.20  
  7 purchase totals = $667.64       $729.4875   $729.48   $729.55   $729.40