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	$104.54	12.136%	$117.227	$117.23	$117.25	$117.20
Purchase #2	$125.29	7.297%	$134.4324	$134.43	$134.45	$134.40
Purchase #3	$74.83	3.794%	$77.6691	$77.67	$77.65	$77.70
Purchase #4	$174.30	6.327%	$185.328	$185.33	$185.35	$185.30
Purchase #5	$9.52	9.238%	$10.3995	$10.40	$10.40	$10.40
Purchase #6	$47.43	13.707%	$53.9312	$53.93	$53.95	$53.90
Purchase #7	$63.90	5.382%	$67.3391	$67.34	$67.35	$67.30
7 purchase totals =	$599.81		$646.3263	$646.33	$646.40	$646.20