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 $224.75   5.862%   $237.9248   $237.92   $237.90   $237.90  
  Purchase #2 $234.85   5.758%   $248.3727   $248.37   $248.35   $248.40  
  Purchase #3 $44.93   12.387%   $50.4955   $50.50   $50.50   $50.50  
  Purchase #4 $28.65   3.417%   $29.629   $29.63   $29.65   $29.60  
  Purchase #5 $159.81   11.470%   $178.1402   $178.14   $178.15   $178.10  
  Purchase #6 $96.68   12.295%   $108.5668   $108.57   $108.55   $108.60  
  Purchase #7 $15.36   7.393%   $16.4956   $16.50   $16.50   $16.50  
  7 purchase totals = $805.03       $869.6246   $869.63   $869.60   $869.60