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	$248.42	10.774%	$275.1848	$275.18	$275.20	$275.20
Purchase #2	$88.50	13.128%	$100.1183	$100.12	$100.10	$100.10
Purchase #3	$11.33	5.569%	$11.961	$11.96	$11.95	$12.00
Purchase #4	$145.32	3.873%	$150.9482	$150.95	$150.95	$150.90
Purchase #5	$47.57	12.820%	$53.6685	$53.67	$53.65	$53.70
Purchase #6	$158.32	5.683%	$167.3173	$167.32	$167.30	$167.30
Purchase #7	$137.92	9.303%	$150.7507	$150.75	$150.75	$150.80
7 purchase totals =	$837.38		$909.9488	$909.95	$909.90	$910.00