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	$53.48	5.830%	$56.5979	$56.60	$56.60	$56.60
Purchase #2	$153.45	12.793%	$173.0809	$173.08	$173.10	$173.10
Purchase #3	$70.89	10.542%	$78.3632	$78.36	$78.35	$78.40
Purchase #4	$152.65	9.707%	$167.4677	$167.47	$167.45	$167.50
Purchase #5	$22.30	8.627%	$24.2238	$24.22	$24.20	$24.20
Purchase #6	$61.29	6.712%	$65.4038	$65.40	$65.40	$65.40
Purchase #7	$11.38	9.484%	$12.4593	$12.46	$12.45	$12.50
7 purchase totals =	$525.44		$577.5966	$577.59	$577.55	$577.70