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 $219.25   10.266%   $241.7582   $241.76   $241.75   $241.80  
  Purchase #2 $18.60   8.567%   $20.1935   $20.19   $20.20   $20.20  
  Purchase #3 $182.64   3.318%   $188.7   $188.70   $188.70   $188.70  
  Purchase #4 $232.70   9.191%   $254.0875   $254.09   $254.10   $254.10  
  Purchase #5 $44.71   12.743%   $50.4074   $50.41   $50.40   $50.40  
  Purchase #6 $132.95   7.451%   $142.8561   $142.86   $142.85   $142.90  
  Purchase #7 $128.78   8.468%   $139.6851   $139.69   $139.70   $139.70  
  7 purchase totals = $959.63       $1,037.6878   $1,037.70   $1,037.70   $1,037.80