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 $192.59   7.344%   $206.7338   $206.73   $206.75   $206.70  
  Purchase #2 $24.76   3.105%   $25.5288   $25.53   $25.55   $25.50  
  Purchase #3 $117.89   10.595%   $130.3804   $130.38   $130.40   $130.40  
  Purchase #4 $67.92   4.556%   $71.0144   $71.01   $71.00   $71.00  
  Purchase #5 $164.42   11.622%   $183.5289   $183.53   $183.55   $183.50  
  Purchase #6 $249.31   4.385%   $260.2422   $260.24   $260.25   $260.20  
  Purchase #7 $208.44   9.145%   $227.5018   $227.50   $227.50   $227.50  
  7 purchase totals = $1,025.33       $1,104.9303   $1,104.92   $1,105.00   $1,104.80