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	$103.98	4.142%	$108.2869	$108.29	$108.30	$108.30
Purchase #2	$214.85	8.763%	$233.6773	$233.68	$233.70	$233.70
Purchase #3	$81.29	6.122%	$86.2666	$86.27	$86.25	$86.30
Purchase #4	$105.27	11.468%	$117.3424	$117.34	$117.35	$117.30
Purchase #5	$131.96	9.112%	$143.9842	$143.98	$144.00	$144.00
Purchase #6	$37.69	10.504%	$41.649	$41.65	$41.65	$41.60
Purchase #7	$238.52	10.337%	$263.1758	$263.18	$263.20	$263.20
7 purchase totals =	$913.56		$994.3822	$994.39	$994.45	$994.40