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 $73.82   3.301%   $76.2568   $76.26   $76.25   $76.30  
  Purchase #2 $76.36   12.470%   $85.8821   $85.88   $85.90   $85.90  
  Purchase #3 $183.91   10.249%   $202.7589   $202.76   $202.75   $202.80  
  Purchase #4 $91.51   7.725%   $98.5791   $98.58   $98.60   $98.60  
  Purchase #5 $82.26   13.730%   $93.5543   $93.55   $93.55   $93.60  
  Purchase #6 $136.46   5.702%   $144.2409   $144.24   $144.25   $144.20  
  Purchase #7 $223.96   13.365%   $253.8923   $253.89   $253.90   $253.90  
  7 purchase totals = $868.28       $955.1644   $955.16   $955.20   $955.30