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 $92.64   5.824%   $98.0354   $98.04   $98.05   $98.00  
  Purchase #2 $179.85   7.164%   $192.7345   $192.73   $192.75   $192.70  
  Purchase #3 $146.30   10.189%   $161.2065   $161.21   $161.20   $161.20  
  Purchase #4 $239.47   5.323%   $252.217   $252.22   $252.20   $252.20  
  Purchase #5 $48.49   9.567%   $53.129   $53.13   $53.15   $53.10  
  Purchase #6 $234.40   10.771%   $259.6472   $259.65   $259.65   $259.60  
  Purchase #7 $18.71   9.216%   $20.4343   $20.43   $20.45   $20.40  
  7 purchase totals = $959.86       $1,037.4039   $1,037.41   $1,037.45   $1,037.20