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	$90.87	7.638%	$97.8107	$97.81	$97.80	$97.80
Purchase #2	$13.38	3.516%	$13.8504	$13.85	$13.85	$13.90
Purchase #3	$156.82	5.376%	$165.2506	$165.25	$165.25	$165.30
Purchase #4	$239.37	3.759%	$248.3679	$248.37	$248.35	$248.40
Purchase #5	$228.77	8.667%	$248.5975	$248.60	$248.60	$248.60
Purchase #6	$100.86	10.536%	$111.4866	$111.49	$111.50	$111.50
Purchase #7	$77.71	13.575%	$88.2591	$88.26	$88.25	$88.30
7 purchase totals =	$907.78		$973.6228	$973.63	$973.60	$973.80