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	$229.69	12.103%	$257.4894	$257.49	$257.50	$257.50
Purchase #2	$122.52	6.534%	$130.5255	$130.53	$130.55	$130.50
Purchase #3	$135.33	7.446%	$145.4067	$145.41	$145.40	$145.40
Purchase #4	$132.54	10.287%	$146.1744	$146.17	$146.15	$146.20
Purchase #5	$87.25	12.628%	$98.2679	$98.27	$98.25	$98.30
Purchase #6	$65.59	7.648%	$70.6063	$70.61	$70.60	$70.60
Purchase #7	$235.51	9.739%	$258.4463	$258.45	$258.45	$258.40
7 purchase totals =	$1,008.43		$1,106.9165	$1,106.93	$1,106.90	$1,106.90