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	$28.58	4.174%	$29.7729	$29.77	$29.75	$29.80
Purchase #2	$155.83	9.425%	$170.517	$170.52	$170.50	$170.50
Purchase #3	$23.87	4.199%	$24.8723	$24.87	$24.85	$24.90
Purchase #4	$215.43	13.521%	$244.5583	$244.56	$244.55	$244.60
Purchase #5	$65.52	10.151%	$72.1709	$72.17	$72.15	$72.20
Purchase #6	$100.55	5.232%	$105.8108	$105.81	$105.80	$105.80
Purchase #7	$24.49	13.312%	$27.7501	$27.75	$27.75	$27.80
7 purchase totals =	$614.27		$675.4523	$675.45	$675.35	$675.60