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	$136.53	12.485%	$153.5758	$153.58	$153.60	$153.60
Purchase #2	$30.49	8.821%	$33.1795	$33.18	$33.20	$33.20
Purchase #3	$29.59	10.733%	$32.7659	$32.77	$32.75	$32.80
Purchase #4	$144.98	6.580%	$154.5197	$154.52	$154.50	$154.50
Purchase #5	$207.50	10.737%	$229.7793	$229.78	$229.80	$229.80
Purchase #6	$101.29	3.650%	$104.9871	$104.99	$105.00	$105.00
Purchase #7	$120.95	5.543%	$127.6543	$127.65	$127.65	$127.70
7 purchase totals =	$771.33		$836.4616	$836.47	$836.50	$836.60