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	$99.97	5.761%	$105.7293	$105.73	$105.75	$105.70
Purchase #2	$214.59	3.738%	$222.6114	$222.61	$222.60	$222.60
Purchase #3	$101.52	6.250%	$107.865	$107.87	$107.85	$107.90
Purchase #4	$110.95	8.665%	$120.5638	$120.56	$120.55	$120.60
Purchase #5	$77.65	9.786%	$85.2488	$85.25	$85.25	$85.20
Purchase #6	$177.52	13.180%	$200.9171	$200.92	$200.90	$200.90
Purchase #7	$50.86	10.532%	$56.2166	$56.22	$56.20	$56.20
7 purchase totals =	$833.06		$899.1520	$899.16	$899.10	$899.10