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 $239.89   9.599%   $262.917   $262.92   $262.90   $262.90  
  Purchase #2 $89.35   10.124%   $98.3958   $98.40   $98.40   $98.40  
  Purchase #3 $109.93   13.454%   $124.72   $124.72   $124.70   $124.70  
  Purchase #4 $187.94   3.293%   $194.1289   $194.13   $194.15   $194.10  
  Purchase #5 $118.80   5.440%   $125.2627   $125.26   $125.25   $125.30  
  Purchase #6 $89.25   13.219%   $101.048   $101.05   $101.05   $101.00  
  Purchase #7 $153.67   5.613%   $162.2955   $162.30   $162.30   $162.30  
  7 purchase totals = $988.83       $1,068.7679   $1,068.78   $1,068.75   $1,068.70