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	$179.82	3.630%	$186.3475	$186.35	$186.35	$186.30
Purchase #2	$92.90	13.557%	$105.4945	$105.49	$105.50	$105.50
Purchase #3	$141.53	11.788%	$158.2136	$158.21	$158.20	$158.20
Purchase #4	$151.26	5.308%	$159.2889	$159.29	$159.30	$159.30
Purchase #5	$78.85	5.846%	$83.4596	$83.46	$83.45	$83.50
Purchase #6	$202.88	8.265%	$219.648	$219.65	$219.65	$219.60
Purchase #7	$49.78	6.731%	$53.1307	$53.13	$53.15	$53.10
7 purchase totals =	$897.02		$965.5828	$965.58	$965.60	$965.50