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	$199.53	12.229%	$223.9305	$223.93	$223.95	$223.90
Purchase #2	$65.45	3.596%	$67.8036	$67.80	$67.80	$67.80
Purchase #3	$158.32	9.586%	$173.4966	$173.50	$173.50	$173.50
Purchase #4	$18.54	7.560%	$19.9416	$19.94	$19.95	$19.90
Purchase #5	$141.94	12.491%	$159.6697	$159.67	$159.65	$159.70
Purchase #6	$45.86	10.735%	$50.7831	$50.78	$50.80	$50.80
Purchase #7	$98.63	13.109%	$111.5594	$111.56	$111.55	$111.60
7 purchase totals =	$728.27		$807.1845	$807.18	$807.20	$807.20