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 $70.56   11.627%   $78.764   $78.76   $78.75   $78.80  
  Purchase #2 $141.57   6.698%   $151.0524   $151.05   $151.05   $151.10  
  Purchase #3 $205.64   6.484%   $218.9737   $218.97   $218.95   $219.00  
  Purchase #4 $116.76   4.138%   $121.5915   $121.59   $121.60   $121.60  
  Purchase #5 $199.73   6.779%   $213.2697   $213.27   $213.25   $213.30  
  Purchase #6 $53.57   13.223%   $60.6536   $60.65   $60.65   $60.70  
  Purchase #7 $99.41   13.195%   $112.5271   $112.53   $112.55   $112.50  
  7 purchase totals = $887.24       $956.8320   $956.82   $956.80   $957.00