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	$48.71	12.753%	$54.922	$54.92	$54.90	$54.90
Purchase #2	$107.31	5.698%	$113.4245	$113.42	$113.40	$113.40
Purchase #3	$49.68	13.669%	$56.4708	$56.47	$56.45	$56.50
Purchase #4	$81.36	10.416%	$89.8345	$89.83	$89.85	$89.80
Purchase #5	$215.90	8.437%	$234.1155	$234.12	$234.10	$234.10
Purchase #6	$91.62	7.497%	$98.4888	$98.49	$98.50	$98.50
Purchase #7	$12.47	6.717%	$13.3076	$13.31	$13.30	$13.30
7 purchase totals =	$607.05		$660.5637	$660.56	$660.50	$660.50