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	$90.29	10.352%	$99.6368	$99.64	$99.65	$99.60
Purchase #2	$133.55	11.805%	$149.3156	$149.32	$149.30	$149.30
Purchase #3	$22.52	12.241%	$25.2767	$25.28	$25.30	$25.30
Purchase #4	$157.50	10.433%	$173.932	$173.93	$173.95	$173.90
Purchase #5	$219.86	11.693%	$245.5682	$245.57	$245.55	$245.60
Purchase #6	$101.50	9.819%	$111.4663	$111.47	$111.45	$111.50
Purchase #7	$34.48	7.579%	$37.0932	$37.09	$37.10	$37.10
7 purchase totals =	$759.70		$842.2888	$842.30	$842.30	$842.30