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	$154.85	10.159%	$170.5812	$170.58	$170.60	$170.60
Purchase #2	$102.32	13.244%	$115.8713	$115.87	$115.85	$115.90
Purchase #3	$20.47	8.530%	$22.2161	$22.22	$22.20	$22.20
Purchase #4	$85.72	4.435%	$89.5217	$89.52	$89.50	$89.50
Purchase #5	$72.32	13.310%	$81.9458	$81.95	$81.95	$81.90
Purchase #6	$53.71	4.770%	$56.272	$56.27	$56.25	$56.30
Purchase #7	$137.27	11.510%	$153.0698	$153.07	$153.05	$153.10
7 purchase totals =	$626.66		$689.4779	$689.48	$689.40	$689.50