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	$90.44	10.285%	$99.7418	$99.74	$99.75	$99.70
Purchase #2	$53.90	10.418%	$59.5153	$59.52	$59.50	$59.50
Purchase #3	$99.49	7.230%	$106.6831	$106.68	$106.70	$106.70
Purchase #4	$188.99	11.548%	$210.8146	$210.81	$210.80	$210.80
Purchase #5	$64.28	3.322%	$66.4154	$66.42	$66.40	$66.40
Purchase #6	$202.92	9.195%	$221.5785	$221.58	$221.60	$221.60
Purchase #7	$123.73	8.700%	$134.4945	$134.49	$134.50	$134.50
7 purchase totals =	$823.75		$899.2432	$899.24	$899.25	$899.20