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 $53.30   7.872%   $57.4958   $57.50   $57.50   $57.50  
  Purchase #2 $197.38   8.756%   $214.6626   $214.66   $214.65   $214.70  
  Purchase #3 $143.76   10.184%   $158.4005   $158.40   $158.40   $158.40  
  Purchase #4 $240.98   3.843%   $250.2409   $250.24   $250.25   $250.20  
  Purchase #5 $133.75   10.513%   $147.8111   $147.81   $147.80   $147.80  
  Purchase #6 $177.48   9.778%   $194.834   $194.83   $194.85   $194.80  
  Purchase #7 $139.53   8.687%   $151.651   $151.65   $151.65   $151.70  
  7 purchase totals = $1,086.18       $1,175.0959   $1,175.09   $1,175.10   $1,175.10