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	$54.92	6.707%	$58.6035	$58.60	$58.60	$58.60
Purchase #2	$146.62	6.127%	$155.6034	$155.60	$155.60	$155.60
Purchase #3	$164.95	5.243%	$173.5983	$173.60	$173.60	$173.60
Purchase #4	$145.29	6.440%	$154.6467	$154.65	$154.65	$154.60
Purchase #5	$117.34	8.332%	$127.1168	$127.12	$127.10	$127.10
Purchase #6	$40.95	7.134%	$43.8714	$43.87	$43.85	$43.90
Purchase #7	$200.80	12.125%	$225.147	$225.15	$225.15	$225.10
7 purchase totals =	$870.87		$938.5871	$938.59	$938.55	$938.50