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	$128.90	11.240%	$143.3884	$143.39	$143.40	$143.40
Purchase #2	$141.89	3.242%	$146.4901	$146.49	$146.50	$146.50
Purchase #3	$105.96	4.762%	$111.0058	$111.01	$111.00	$111.00
Purchase #4	$11.30	13.107%	$12.7811	$12.78	$12.80	$12.80
Purchase #5	$110.90	6.240%	$117.8202	$117.82	$117.80	$117.80
Purchase #6	$21.27	13.347%	$24.1089	$24.11	$24.10	$24.10
Purchase #7	$114.45	7.613%	$123.1631	$123.16	$123.15	$123.20
7 purchase totals =	$634.67		$678.7576	$678.76	$678.75	$678.80