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	$52.43	11.513%	$58.4663	$58.47	$58.45	$58.50
Purchase #2	$84.99	5.353%	$89.5395	$89.54	$89.55	$89.50
Purchase #3	$204.97	9.515%	$224.4729	$224.47	$224.45	$224.50
Purchase #4	$19.45	6.179%	$20.6518	$20.65	$20.65	$20.70
Purchase #5	$165.35	10.525%	$182.7531	$182.75	$182.75	$182.80
Purchase #6	$9.75	9.495%	$10.6758	$10.68	$10.70	$10.70
Purchase #7	$190.52	3.187%	$196.5919	$196.59	$196.60	$196.60
7 purchase totals =	$727.46		$783.1513	$783.15	$783.15	$783.30