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	$222.53	10.831%	$246.6322	$246.63	$246.65	$246.60
Purchase #2	$52.69	6.560%	$56.1465	$56.15	$56.15	$56.10
Purchase #3	$18.45	8.503%	$20.0188	$20.02	$20.00	$20.00
Purchase #4	$36.55	11.583%	$40.7836	$40.78	$40.80	$40.80
Purchase #5	$153.68	7.642%	$165.4242	$165.42	$165.40	$165.40
Purchase #6	$29.94	11.162%	$33.2819	$33.28	$33.30	$33.30
Purchase #7	$37.69	6.361%	$40.0875	$40.09	$40.10	$40.10
7 purchase totals =	$551.53		$602.3747	$602.37	$602.40	$602.30