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	$39.58	8.793%	$43.0603	$43.06	$43.05	$43.10
Purchase #2	$136.75	5.212%	$143.8774	$143.88	$143.90	$143.90
Purchase #3	$10.38	3.845%	$10.7791	$10.78	$10.80	$10.80
Purchase #4	$144.94	13.868%	$165.0403	$165.04	$165.05	$165.00
Purchase #5	$90.46	5.171%	$95.1377	$95.14	$95.15	$95.10
Purchase #6	$94.90	7.307%	$101.8343	$101.83	$101.85	$101.80
Purchase #7	$129.68	6.846%	$138.5579	$138.56	$138.55	$138.60
7 purchase totals =	$646.69		$698.2870	$698.29	$698.35	$698.30