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	$79.42	13.256%	$89.9479	$89.95	$89.95	$89.90
Purchase #2	$121.95	4.810%	$127.8158	$127.82	$127.80	$127.80
Purchase #3	$93.67	6.790%	$100.0302	$100.03	$100.05	$100.00
Purchase #4	$189.68	5.777%	$200.6378	$200.64	$200.65	$200.60
Purchase #5	$37.52	4.713%	$39.2883	$39.29	$39.30	$39.30
Purchase #6	$74.41	10.871%	$82.4991	$82.50	$82.50	$82.50
Purchase #7	$124.55	8.175%	$134.732	$134.73	$134.75	$134.70
7 purchase totals =	$721.20		$774.9511	$774.96	$775.00	$774.80