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	$50.91	3.126%	$52.5014	$52.50	$52.50	$52.50
Purchase #2	$145.61	9.136%	$158.9129	$158.91	$158.90	$158.90
Purchase #3	$196.52	9.339%	$214.873	$214.87	$214.85	$214.90
Purchase #4	$99.29	5.753%	$105.0022	$105.00	$105.00	$105.00
Purchase #5	$127.43	13.243%	$144.3056	$144.31	$144.30	$144.30
Purchase #6	$233.98	11.300%	$260.4197	$260.42	$260.40	$260.40
Purchase #7	$136.71	4.518%	$142.8866	$142.89	$142.90	$142.90
7 purchase totals =	$990.45		$1,078.9014	$1,078.90	$1,078.85	$1,078.90