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	$59.44	10.843%	$65.8851	$65.89	$65.90	$65.90
Purchase #2	$128.93	7.843%	$139.042	$139.04	$139.05	$139.00
Purchase #3	$18.79	7.520%	$20.203	$20.20	$20.20	$20.20
Purchase #4	$216.39	10.708%	$239.561	$239.56	$239.55	$239.60
Purchase #5	$87.58	13.363%	$99.2833	$99.28	$99.30	$99.30
Purchase #6	$178.44	8.206%	$193.0828	$193.08	$193.10	$193.10
Purchase #7	$82.72	9.734%	$90.772	$90.77	$90.75	$90.80
7 purchase totals =	$772.29		$847.8292	$847.82	$847.85	$847.90