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	$43.98	10.237%	$48.4822	$48.48	$48.50	$48.50
Purchase #2	$125.78	9.449%	$137.665	$137.67	$137.65	$137.70
Purchase #3	$114.55	11.371%	$127.5755	$127.58	$127.60	$127.60
Purchase #4	$56.82	3.204%	$58.6405	$58.64	$58.65	$58.60
Purchase #5	$141.71	3.111%	$146.1186	$146.12	$146.10	$146.10
Purchase #6	$174.93	6.443%	$186.2007	$186.20	$186.20	$186.20
Purchase #7	$239.39	10.499%	$264.5236	$264.52	$264.50	$264.50
7 purchase totals =	$897.16		$969.2061	$969.21	$969.20	$969.20