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	$88.65	13.537%	$100.6506	$100.65	$100.65	$100.70
Purchase #2	$221.95	10.325%	$244.8663	$244.87	$244.85	$244.90
Purchase #3	$227.52	13.590%	$258.44	$258.44	$258.45	$258.40
Purchase #4	$172.91	13.512%	$196.2736	$196.27	$196.25	$196.30
Purchase #5	$248.59	11.383%	$276.887	$276.89	$276.90	$276.90
Purchase #6	$78.26	11.864%	$87.5448	$87.54	$87.55	$87.50
Purchase #7	$132.28	9.617%	$145.0014	$145.00	$145.00	$145.00
7 purchase totals =	$1,170.16		$1,309.6637	$1,309.66	$1,309.65	$1,309.70