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	$9.31	10.588%	$10.2957	$10.30	$10.30	$10.30
Purchase #2	$79.60	12.567%	$89.6033	$89.60	$89.60	$89.60
Purchase #3	$226.42	13.194%	$256.2939	$256.29	$256.30	$256.30
Purchase #4	$65.47	3.130%	$67.5192	$67.52	$67.50	$67.50
Purchase #5	$91.74	3.817%	$95.2417	$95.24	$95.25	$95.20
Purchase #6	$6.71	8.667%	$7.2916	$7.29	$7.30	$7.30
Purchase #7	$130.90	6.729%	$139.7083	$139.71	$139.70	$139.70
7 purchase totals =	$610.15		$665.9537	$665.95	$665.95	$665.90