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 $163.38   3.201%   $168.6098   $168.61   $168.60   $168.60  
  Purchase #2 $239.47   11.207%   $266.3074   $266.31   $266.30   $266.30  
  Purchase #3 $175.62   11.518%   $195.8479   $195.85   $195.85   $195.80  
  Purchase #4 $61.67   4.516%   $64.455   $64.46   $64.45   $64.50  
  Purchase #5 $160.81   13.871%   $183.116   $183.12   $183.10   $183.10  
  Purchase #6 $109.96   7.268%   $117.9519   $117.95   $117.95   $118.00  
  Purchase #7 $180.99   4.769%   $189.6214   $189.62   $189.60   $189.60  
  7 purchase totals = $1,091.90       $1,185.9094   $1,185.92   $1,185.85   $1,185.90