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	$34.87	7.347%	$37.4319	$37.43	$37.45	$37.40
Purchase #2	$237.45	11.453%	$264.6451	$264.65	$264.65	$264.60
Purchase #3	$139.71	13.116%	$158.0344	$158.03	$158.05	$158.00
Purchase #4	$145.34	13.845%	$165.4623	$165.46	$165.45	$165.50
Purchase #5	$51.36	4.797%	$53.8237	$53.82	$53.80	$53.80
Purchase #6	$6.28	8.143%	$6.7914	$6.79	$6.80	$6.80
Purchase #7	$50.25	12.126%	$56.3433	$56.34	$56.35	$56.30
7 purchase totals =	$665.26		$742.5321	$742.52	$742.55	$742.40