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	$37.83	11.773%	$42.2837	$42.28	$42.30	$42.30
Purchase #2	$27.26	3.494%	$28.2125	$28.21	$28.20	$28.20
Purchase #3	$16.67	13.445%	$18.9113	$18.91	$18.90	$18.90
Purchase #4	$127.79	13.725%	$145.3292	$145.33	$145.35	$145.30
Purchase #5	$25.67	6.332%	$27.2954	$27.30	$27.30	$27.30
Purchase #6	$107.31	3.714%	$111.2955	$111.30	$111.30	$111.30
Purchase #7	$9.71	9.110%	$10.5946	$10.59	$10.60	$10.60
7 purchase totals =	$352.24		$383.9222	$383.92	$383.95	$383.90