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	$144.75	10.439%	$159.8605	$159.86	$159.85	$159.90
Purchase #2	$142.88	6.715%	$152.4744	$152.47	$152.45	$152.50
Purchase #3	$37.86	7.249%	$40.6045	$40.60	$40.60	$40.60
Purchase #4	$28.83	13.251%	$32.6503	$32.65	$32.65	$32.70
Purchase #5	$143.25	12.661%	$161.3869	$161.39	$161.40	$161.40
Purchase #6	$57.50	5.213%	$60.4975	$60.50	$60.50	$60.50
Purchase #7	$34.77	13.220%	$39.3666	$39.37	$39.35	$39.40
7 purchase totals =	$589.84		$646.8407	$646.84	$646.80	$647.00