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	$107.77	3.495%	$111.5366	$111.54	$111.55	$111.50
Purchase #2	$122.91	11.434%	$136.9635	$136.96	$136.95	$137.00
Purchase #3	$163.58	7.156%	$175.2858	$175.29	$175.30	$175.30
Purchase #4	$95.50	10.626%	$105.6478	$105.65	$105.65	$105.60
Purchase #5	$31.89	4.437%	$33.305	$33.31	$33.30	$33.30
Purchase #6	$157.76	5.652%	$166.6766	$166.68	$166.70	$166.70
Purchase #7	$70.35	5.443%	$74.1792	$74.18	$74.20	$74.20
7 purchase totals =	$749.76		$803.5945	$803.61	$803.65	$803.60