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	$67.37	8.852%	$73.3336	$73.33	$73.35	$73.30
Purchase #2	$141.36	11.141%	$157.1089	$157.11	$157.10	$157.10
Purchase #3	$62.37	12.681%	$70.2791	$70.28	$70.30	$70.30
Purchase #4	$173.58	6.521%	$184.8992	$184.90	$184.90	$184.90
Purchase #5	$138.51	9.578%	$151.7765	$151.78	$151.80	$151.80
Purchase #6	$140.61	13.716%	$159.8961	$159.90	$159.90	$159.90
Purchase #7	$38.92	8.696%	$42.3045	$42.30	$42.30	$42.30
7 purchase totals =	$762.72		$839.5979	$839.60	$839.65	$839.60