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	$30.96	13.604%	$35.1718	$35.17	$35.15	$35.20
Purchase #2	$46.89	5.505%	$49.4713	$49.47	$49.45	$49.50
Purchase #3	$124.45	11.685%	$138.992	$138.99	$139.00	$139.00
Purchase #4	$242.83	11.556%	$270.8914	$270.89	$270.90	$270.90
Purchase #5	$19.49	4.772%	$20.4201	$20.42	$20.40	$20.40
Purchase #6	$13.93	9.356%	$15.2333	$15.23	$15.25	$15.20
Purchase #7	$54.85	11.617%	$61.2219	$61.22	$61.20	$61.20
7 purchase totals =	$533.40		$591.4018	$591.39	$591.35	$591.40