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	$50.35	9.491%	$55.1287	$55.13	$55.15	$55.10
Purchase #2	$83.64	10.440%	$92.372	$92.37	$92.35	$92.40
Purchase #3	$89.39	10.866%	$99.1031	$99.10	$99.10	$99.10
Purchase #4	$120.59	5.572%	$127.3093	$127.31	$127.30	$127.30
Purchase #5	$136.83	7.131%	$146.5873	$146.59	$146.60	$146.60
Purchase #6	$139.37	8.719%	$151.5217	$151.52	$151.50	$151.50
Purchase #7	$87.88	9.409%	$96.1486	$96.15	$96.15	$96.10
7 purchase totals =	$708.05		$768.1707	$768.17	$768.15	$768.10