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	$51.87	4.778%	$54.3483	$54.35	$54.35	$54.30
Purchase #2	$29.81	11.650%	$33.2829	$33.28	$33.30	$33.30
Purchase #3	$86.83	5.321%	$91.4502	$91.45	$91.45	$91.50
Purchase #4	$16.95	3.584%	$17.5575	$17.56	$17.55	$17.60
Purchase #5	$111.32	10.856%	$123.4049	$123.40	$123.40	$123.40
Purchase #6	$106.87	12.161%	$119.8665	$119.87	$119.85	$119.90
Purchase #7	$207.83	3.741%	$215.6049	$215.60	$215.60	$215.60
7 purchase totals =	$611.48		$655.5152	$655.51	$655.50	$655.60