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	$105.54	6.581%	$112.4856	$112.49	$112.50	$112.50
Purchase #2	$243.76	4.869%	$255.6287	$255.63	$255.65	$255.60
Purchase #3	$52.90	10.592%	$58.5032	$58.50	$58.50	$58.50
Purchase #4	$140.66	8.667%	$152.851	$152.85	$152.85	$152.90
Purchase #5	$94.52	11.739%	$105.6157	$105.62	$105.60	$105.60
Purchase #6	$149.35	6.672%	$159.3146	$159.31	$159.30	$159.30
Purchase #7	$58.29	8.572%	$63.2866	$63.29	$63.30	$63.30
7 purchase totals =	$845.02		$907.6854	$907.69	$907.70	$907.70