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	$165.78	9.858%	$182.1226	$182.12	$182.10	$182.10
Purchase #2	$58.92	13.205%	$66.7004	$66.70	$66.70	$66.70
Purchase #3	$234.52	3.228%	$242.0903	$242.09	$242.10	$242.10
Purchase #4	$78.50	10.268%	$86.5604	$86.56	$86.55	$86.60
Purchase #5	$105.41	5.584%	$111.2961	$111.30	$111.30	$111.30
Purchase #6	$56.48	5.225%	$59.4311	$59.43	$59.45	$59.40
Purchase #7	$49.82	8.233%	$53.9217	$53.92	$53.90	$53.90
7 purchase totals =	$749.43		$802.1226	$802.12	$802.10	$802.10