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	$32.84	11.754%	$36.7	$36.70	$36.70	$36.70
Purchase #2	$184.86	5.365%	$194.7777	$194.78	$194.80	$194.80
Purchase #3	$80.67	11.570%	$90.0035	$90.00	$90.00	$90.00
Purchase #4	$233.86	12.251%	$262.5102	$262.51	$262.50	$262.50
Purchase #5	$149.78	7.703%	$161.3176	$161.32	$161.30	$161.30
Purchase #6	$85.66	5.677%	$90.5229	$90.52	$90.50	$90.50
Purchase #7	$152.83	4.544%	$159.7746	$159.77	$159.75	$159.80
7 purchase totals =	$920.50		$995.6065	$995.60	$995.55	$995.60