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	$98.82	4.768%	$103.5317	$103.53	$103.55	$103.50
Purchase #2	$218.52	12.417%	$245.6536	$245.65	$245.65	$245.70
Purchase #3	$83.51	12.346%	$93.8201	$93.82	$93.80	$93.80
Purchase #4	$31.83	6.514%	$33.9034	$33.90	$33.90	$33.90
Purchase #5	$27.68	13.874%	$31.5203	$31.52	$31.50	$31.50
Purchase #6	$131.81	6.223%	$140.0125	$140.01	$140.00	$140.00
Purchase #7	$31.43	8.810%	$34.199	$34.20	$34.20	$34.20
7 purchase totals =	$623.60		$682.6406	$682.63	$682.60	$682.60