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	$50.97	5.621%	$53.835	$53.84	$53.85	$53.80
Purchase #2	$241.65	3.680%	$250.5427	$250.54	$250.55	$250.50
Purchase #3	$28.27	11.710%	$31.5804	$31.58	$31.60	$31.60
Purchase #4	$190.38	12.823%	$214.7924	$214.79	$214.80	$214.80
Purchase #5	$221.88	3.521%	$229.6924	$229.69	$229.70	$229.70
Purchase #6	$122.89	13.265%	$139.1914	$139.19	$139.20	$139.20
Purchase #7	$29.38	12.773%	$33.1327	$33.13	$33.15	$33.10
7 purchase totals =	$885.42		$952.7670	$952.76	$952.85	$952.70