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	$78.88	5.825%	$83.4748	$83.47	$83.45	$83.50
Purchase #2	$57.26	5.798%	$60.5799	$60.58	$60.60	$60.60
Purchase #3	$224.59	11.707%	$250.8828	$250.88	$250.90	$250.90
Purchase #4	$150.49	11.474%	$167.7572	$167.76	$167.75	$167.80
Purchase #5	$32.88	13.392%	$37.2833	$37.28	$37.30	$37.30
Purchase #6	$106.25	5.106%	$111.6751	$111.68	$111.70	$111.70
Purchase #7	$129.43	11.236%	$143.9728	$143.97	$143.95	$144.00
7 purchase totals =	$779.78		$855.6259	$855.62	$855.65	$855.80