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 $54.25   11.806%   $60.6548   $60.65   $60.65   $60.70  
  Purchase #2 $16.92   10.135%   $18.6348   $18.63   $18.65   $18.60  
  Purchase #3 $46.95   5.684%   $49.6186   $49.62   $49.60   $49.60  
  Purchase #4 $101.79   5.569%   $107.4587   $107.46   $107.45   $107.50  
  Purchase #5 $28.73   9.188%   $31.3697   $31.37   $31.35   $31.40  
  Purchase #6 $19.99   4.135%   $20.8166   $20.82   $20.80   $20.80  
  Purchase #7 $199.75   4.409%   $208.557   $208.56   $208.55   $208.60  
  7 purchase totals = $468.38       $497.1102   $497.11   $497.05   $497.20