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	$230.44	7.222%	$247.0824	$247.08	$247.10	$247.10
Purchase #2	$148.44	3.571%	$153.7408	$153.74	$153.75	$153.70
Purchase #3	$193.42	12.482%	$217.5627	$217.56	$217.55	$217.60
Purchase #4	$134.35	9.311%	$146.8593	$146.86	$146.85	$146.90
Purchase #5	$128.92	12.588%	$145.1484	$145.15	$145.15	$145.10
Purchase #6	$116.87	13.709%	$132.8917	$132.89	$132.90	$132.90
Purchase #7	$54.83	13.274%	$62.1081	$62.11	$62.10	$62.10
7 purchase totals =	$1,007.27		$1,105.3934	$1,105.39	$1,105.40	$1,105.40