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	$143.94	4.366%	$150.2244	$150.22	$150.20	$150.20
Purchase #2	$89.42	10.866%	$99.1364	$99.14	$99.15	$99.10
Purchase #3	$214.53	3.291%	$221.5902	$221.59	$221.60	$221.60
Purchase #4	$26.47	12.196%	$29.6983	$29.70	$29.70	$29.70
Purchase #5	$144.75	3.236%	$149.4341	$149.43	$149.45	$149.40
Purchase #6	$152.83	7.745%	$164.6667	$164.67	$164.65	$164.70
Purchase #7	$91.65	9.693%	$100.5336	$100.53	$100.55	$100.50
7 purchase totals =	$863.59		$915.2837	$915.28	$915.30	$915.20