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 $200.89   12.116%   $225.2298   $225.23   $225.25   $225.20  
  Purchase #2 $202.31   4.186%   $210.7787   $210.78   $210.80   $210.80  
  Purchase #3 $153.65   10.622%   $169.9707   $169.97   $169.95   $170.00  
  Purchase #4 $250.78   10.562%   $277.2674   $277.27   $277.25   $277.30  
  Purchase #5 $61.33   3.183%   $63.2821   $63.28   $63.30   $63.30  
  Purchase #6 $244.60   11.810%   $273.4873   $273.49   $273.50   $273.50  
  Purchase #7 $246.34   11.329%   $274.2479   $274.25   $274.25   $274.20  
  7 purchase totals = $1,359.90       $1,494.2639   $1,494.27   $1,494.30   $1,494.30