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	$80.42	11.346%	$89.5445	$89.54	$89.55	$89.50
Purchase #2	$11.52	9.485%	$12.6127	$12.61	$12.60	$12.60
Purchase #3	$249.28	13.830%	$283.7554	$283.76	$283.75	$283.80
Purchase #4	$62.44	4.249%	$65.0931	$65.09	$65.10	$65.10
Purchase #5	$183.41	8.757%	$199.4712	$199.47	$199.45	$199.50
Purchase #6	$177.73	6.141%	$188.6444	$188.64	$188.65	$188.60
Purchase #7	$220.86	6.636%	$235.5163	$235.52	$235.50	$235.50
7 purchase totals =	$985.66		$1,074.6376	$1,074.63	$1,074.60	$1,074.60