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	$32.25	13.189%	$36.5035	$36.50	$36.50	$36.50
Purchase #2	$34.27	7.136%	$36.7155	$36.72	$36.70	$36.70
Purchase #3	$196.52	9.220%	$214.6391	$214.64	$214.65	$214.60
Purchase #4	$37.59	13.789%	$42.7733	$42.77	$42.75	$42.80
Purchase #5	$211.35	7.679%	$227.5796	$227.58	$227.60	$227.60
Purchase #6	$239.86	9.196%	$261.9175	$261.92	$261.90	$261.90
Purchase #7	$184.74	8.317%	$200.1048	$200.10	$200.10	$200.10
7 purchase totals =	$936.58		$1,020.2333	$1,020.23	$1,020.20	$1,020.20