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	$131.77	4.479%	$137.672	$137.67	$137.65	$137.70
Purchase #2	$223.43	12.603%	$251.5889	$251.59	$251.60	$251.60
Purchase #3	$52.83	3.319%	$54.5834	$54.58	$54.60	$54.60
Purchase #4	$185.54	7.714%	$199.8526	$199.85	$199.85	$199.90
Purchase #5	$149.31	5.311%	$157.2399	$157.24	$157.25	$157.20
Purchase #6	$46.56	8.380%	$50.4617	$50.46	$50.45	$50.50
Purchase #7	$227.84	8.735%	$247.7418	$247.74	$247.75	$247.70
7 purchase totals =	$1,017.28		$1,099.1403	$1,099.13	$1,099.15	$1,099.20