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 $118.68   5.680%   $125.421   $125.42   $125.40   $125.40  
  Purchase #2 $162.84   8.451%   $176.6016   $176.60   $176.60   $176.60  
  Purchase #3 $151.74   13.538%   $172.2826   $172.28   $172.30   $172.30  
  Purchase #4 $183.82   12.193%   $206.2332   $206.23   $206.25   $206.20  
  Purchase #5 $151.32   5.763%   $160.0406   $160.04   $160.05   $160.00  
  Purchase #6 $98.67   10.549%   $109.0787   $109.08   $109.10   $109.10  
  Purchase #7 $65.89   5.730%   $69.6655   $69.67   $69.65   $69.70  
  7 purchase totals = $932.96       $1,019.3232   $1,019.32   $1,019.35   $1,019.30