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	$159.87	12.340%	$179.598	$179.60	$179.60	$179.60
Purchase #2	$20.26	3.451%	$20.9592	$20.96	$20.95	$21.00
Purchase #3	$47.38	5.172%	$49.8305	$49.83	$49.85	$49.80
Purchase #4	$7.87	11.163%	$8.7485	$8.75	$8.75	$8.70
Purchase #5	$78.72	4.540%	$82.2939	$82.29	$82.30	$82.30
Purchase #6	$159.56	5.778%	$168.7794	$168.78	$168.80	$168.80
Purchase #7	$213.81	13.565%	$242.8133	$242.81	$242.80	$242.80
7 purchase totals =	$687.47		$753.0228	$753.02	$753.05	$753.00