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 $248.70   6.458%   $264.761   $264.76   $264.75   $264.80  
  Purchase #2 $96.75   4.852%   $101.4443   $101.44   $101.45   $101.40  
  Purchase #3 $90.60   8.123%   $97.9594   $97.96   $97.95   $98.00  
  Purchase #4 $118.73   4.586%   $124.175   $124.18   $124.20   $124.20  
  Purchase #5 $109.26   8.122%   $118.1341   $118.13   $118.15   $118.10  
  Purchase #6 $64.28   5.670%   $67.9247   $67.92   $67.90   $67.90  
  Purchase #7 $64.73   11.147%   $71.9455   $71.95   $71.95   $71.90  
  7 purchase totals = $793.05       $846.3440   $846.34   $846.35   $846.30