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	$87.92	13.215%	$99.5386	$99.54	$99.55	$99.50
Purchase #2	$125.63	10.139%	$138.3676	$138.37	$138.35	$138.40
Purchase #3	$134.96	8.103%	$145.8958	$145.90	$145.90	$145.90
Purchase #4	$129.76	3.692%	$134.5507	$134.55	$134.55	$134.60
Purchase #5	$111.40	11.851%	$124.602	$124.60	$124.60	$124.60
Purchase #6	$92.73	8.874%	$100.9589	$100.96	$100.95	$101.00
Purchase #7	$106.31	10.198%	$117.1515	$117.15	$117.15	$117.20
7 purchase totals =	$788.71		$861.0651	$861.07	$861.05	$861.20