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	$59.89	13.321%	$67.8679	$67.87	$67.85	$67.90
Purchase #2	$162.81	13.699%	$185.1133	$185.11	$185.10	$185.10
Purchase #3	$125.90	8.496%	$136.5965	$136.60	$136.60	$136.60
Purchase #4	$50.58	3.320%	$52.2593	$52.26	$52.25	$52.30
Purchase #5	$172.71	11.735%	$192.9775	$192.98	$193.00	$193.00
Purchase #6	$140.37	9.385%	$153.5437	$153.54	$153.55	$153.50
Purchase #7	$42.70	13.126%	$48.3048	$48.30	$48.30	$48.30
7 purchase totals =	$754.96		$836.6630	$836.66	$836.65	$836.70