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 $241.66   13.690%   $274.7433   $274.74   $274.75   $274.70  
  Purchase #2 $174.47   8.451%   $189.2145   $189.21   $189.20   $189.20  
  Purchase #3 $228.60   11.792%   $255.5565   $255.56   $255.55   $255.60  
  Purchase #4 $99.98   5.223%   $105.202   $105.20   $105.20   $105.20  
  Purchase #5 $81.58   6.312%   $86.7293   $86.73   $86.75   $86.70  
  Purchase #6 $229.73   12.484%   $258.4095   $258.41   $258.40   $258.40  
  Purchase #7 $244.47   7.303%   $262.3236   $262.32   $262.30   $262.30  
  7 purchase totals = $1,300.49       $1,432.1787   $1,432.17   $1,432.15   $1,432.10