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	$108.32	4.240%	$112.9128	$112.91	$112.90	$112.90
Purchase #2	$190.85	7.117%	$204.4328	$204.43	$204.45	$204.40
Purchase #3	$138.53	9.370%	$151.5103	$151.51	$151.50	$151.50
Purchase #4	$35.58	13.698%	$40.4537	$40.45	$40.45	$40.50
Purchase #5	$229.64	12.506%	$258.3588	$258.36	$258.35	$258.40
Purchase #6	$17.84	6.548%	$19.0082	$19.01	$19.00	$19.00
Purchase #7	$53.42	13.460%	$60.6103	$60.61	$60.60	$60.60
7 purchase totals =	$774.18		$847.2869	$847.28	$847.25	$847.30