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	$78.26	13.844%	$89.0943	$89.09	$89.10	$89.10
Purchase #2	$49.87	5.692%	$52.7086	$52.71	$52.70	$52.70
Purchase #3	$156.82	11.685%	$175.1444	$175.14	$175.15	$175.10
Purchase #4	$242.52	4.592%	$253.6565	$253.66	$253.65	$253.70
Purchase #5	$138.38	7.187%	$148.3254	$148.33	$148.35	$148.30
Purchase #6	$196.40	8.325%	$212.7503	$212.75	$212.75	$212.80
Purchase #7	$140.52	8.211%	$152.0581	$152.06	$152.05	$152.10
7 purchase totals =	$1,002.77		$1,083.7376	$1,083.74	$1,083.75	$1,083.80