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	$26.29	12.109%	$29.4735	$29.47	$29.45	$29.50
Purchase #2	$48.78	4.729%	$51.0868	$51.09	$51.10	$51.10
Purchase #3	$57.93	7.765%	$62.4283	$62.43	$62.45	$62.40
Purchase #4	$48.92	8.649%	$53.1511	$53.15	$53.15	$53.20
Purchase #5	$237.64	7.326%	$255.0495	$255.05	$255.05	$255.00
Purchase #6	$146.77	9.665%	$160.9553	$160.96	$160.95	$161.00
Purchase #7	$49.66	11.666%	$55.4533	$55.45	$55.45	$55.50
7 purchase totals =	$615.99		$667.5978	$667.60	$667.60	$667.70