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	$250.28	12.380%	$281.2647	$281.26	$281.25	$281.30
Purchase #2	$83.73	10.449%	$92.4789	$92.48	$92.50	$92.50
Purchase #3	$101.75	6.423%	$108.2854	$108.29	$108.30	$108.30
Purchase #4	$230.79	3.162%	$238.0876	$238.09	$238.10	$238.10
Purchase #5	$106.76	4.276%	$111.3251	$111.33	$111.35	$111.30
Purchase #6	$189.77	7.287%	$203.5985	$203.60	$203.60	$203.60
Purchase #7	$77.92	7.694%	$83.9152	$83.92	$83.90	$83.90
7 purchase totals =	$1,041.00		$1,118.9554	$1,118.97	$1,119.00	$1,119.00