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	$9.33	7.271%	$10.0084	$10.01	$10.00	$10.00
Purchase #2	$151.77	13.570%	$172.3652	$172.37	$172.35	$172.40
Purchase #3	$17.87	11.118%	$19.8568	$19.86	$19.85	$19.90
Purchase #4	$176.52	5.242%	$185.7732	$185.77	$185.75	$185.80
Purchase #5	$72.69	9.618%	$79.6813	$79.68	$79.70	$79.70
Purchase #6	$140.57	13.588%	$159.6707	$159.67	$159.65	$159.70
Purchase #7	$81.53	9.245%	$89.0674	$89.07	$89.05	$89.10
7 purchase totals =	$650.28		$716.4230	$716.43	$716.35	$716.60