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	$48.89	12.823%	$55.1592	$55.16	$55.15	$55.20
Purchase #2	$100.34	5.182%	$105.5396	$105.54	$105.55	$105.50
Purchase #3	$55.36	10.665%	$61.2641	$61.26	$61.25	$61.30
Purchase #4	$123.71	4.167%	$128.865	$128.87	$128.85	$128.90
Purchase #5	$18.34	5.523%	$19.3529	$19.35	$19.35	$19.40
Purchase #6	$33.59	6.797%	$35.8731	$35.87	$35.85	$35.90
Purchase #7	$18.95	9.393%	$20.73	$20.73	$20.75	$20.70
7 purchase totals =	$399.18		$426.7839	$426.78	$426.75	$426.90