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	$97.52	8.615%	$105.9213	$105.92	$105.90	$105.90
Purchase #2	$216.40	7.106%	$231.7774	$231.78	$231.80	$231.80
Purchase #3	$151.54	13.663%	$172.2449	$172.24	$172.25	$172.20
Purchase #4	$211.63	8.414%	$229.4365	$229.44	$229.45	$229.40
Purchase #5	$129.40	7.637%	$139.2823	$139.28	$139.30	$139.30
Purchase #6	$87.27	3.472%	$90.3	$90.30	$90.30	$90.30
Purchase #7	$10.94	5.504%	$11.5421	$11.54	$11.55	$11.50
7 purchase totals =	$904.70		$980.5045	$980.50	$980.55	$980.40