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	$74.69	5.479%	$78.7823	$78.78	$78.80	$78.80
Purchase #2	$91.74	9.717%	$100.6544	$100.65	$100.65	$100.70
Purchase #3	$56.58	6.695%	$60.368	$60.37	$60.35	$60.40
Purchase #4	$95.60	4.178%	$99.5942	$99.59	$99.60	$99.60
Purchase #5	$202.50	11.853%	$226.5023	$226.50	$226.50	$226.50
Purchase #6	$228.33	11.657%	$254.9464	$254.95	$254.95	$254.90
Purchase #7	$33.90	7.428%	$36.4181	$36.42	$36.40	$36.40
7 purchase totals =	$783.34		$857.2657	$857.26	$857.25	$857.30