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	$231.63	9.192%	$252.9214	$252.92	$252.90	$252.90
Purchase #2	$19.71	7.367%	$21.162	$21.16	$21.15	$21.20
Purchase #3	$139.25	13.830%	$158.5083	$158.51	$158.50	$158.50
Purchase #4	$120.90	5.308%	$127.3174	$127.32	$127.30	$127.30
Purchase #5	$134.63	8.292%	$145.7935	$145.79	$145.80	$145.80
Purchase #6	$132.91	13.150%	$150.3877	$150.39	$150.40	$150.40
Purchase #7	$132.58	7.609%	$142.668	$142.67	$142.65	$142.70
7 purchase totals =	$911.61		$998.7583	$998.76	$998.70	$998.80