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 $29.98   11.833%   $33.5275   $33.53   $33.55   $33.50  
  Purchase #2 $246.44   7.381%   $264.6297   $264.63   $264.65   $264.60  
  Purchase #3 $228.36   3.179%   $235.6196   $235.62   $235.60   $235.60  
  Purchase #4 $31.41   9.770%   $34.4788   $34.48   $34.50   $34.50  
  Purchase #5 $245.92   6.489%   $261.8777   $261.88   $261.90   $261.90  
  Purchase #6 $242.89   6.390%   $258.4107   $258.41   $258.40   $258.40  
  Purchase #7 $134.53   7.597%   $144.7502   $144.75   $144.75   $144.80  
  7 purchase totals = $1,159.53       $1,233.2942   $1,233.30   $1,233.35   $1,233.30