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	$9.56	7.162%	$10.2447	$10.24	$10.25	$10.20
Purchase #2	$9.55	7.588%	$10.2747	$10.27	$10.25	$10.30
Purchase #3	$216.89	13.730%	$246.669	$246.67	$246.65	$246.70
Purchase #4	$102.93	8.690%	$111.8746	$111.87	$111.85	$111.90
Purchase #5	$81.64	10.593%	$90.2881	$90.29	$90.30	$90.30
Purchase #6	$168.93	6.718%	$180.2787	$180.28	$180.30	$180.30
Purchase #7	$10.87	12.200%	$12.1961	$12.20	$12.20	$12.20
7 purchase totals =	$600.37		$661.8259	$661.82	$661.80	$661.90