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 $23.95   9.606%   $26.2506   $26.25   $26.25   $26.30  
  Purchase #2 $248.27   12.639%   $279.6488   $279.65   $279.65   $279.60  
  Purchase #3 $23.51   7.384%   $25.246   $25.25   $25.25   $25.20  
  Purchase #4 $249.86   3.330%   $258.1803   $258.18   $258.20   $258.20  
  Purchase #5 $144.84   13.760%   $164.77   $164.77   $164.75   $164.80  
  Purchase #6 $159.61   5.282%   $168.0406   $168.04   $168.05   $168.00  
  Purchase #7 $141.78   11.284%   $157.7785   $157.78   $157.80   $157.80  
  7 purchase totals = $991.82       $1,079.9148   $1,079.92   $1,079.95   $1,079.90