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	$127.59	3.697%	$132.307	$132.31	$132.30	$132.30
Purchase #2	$87.63	4.407%	$91.4919	$91.49	$91.50	$91.50
Purchase #3	$111.87	13.565%	$127.0452	$127.05	$127.05	$127.00
Purchase #4	$48.77	3.714%	$50.5813	$50.58	$50.60	$50.60
Purchase #5	$227.72	11.787%	$254.5614	$254.56	$254.55	$254.60
Purchase #6	$123.45	10.626%	$136.5678	$136.57	$136.55	$136.60
Purchase #7	$193.32	3.186%	$199.4792	$199.48	$199.50	$199.50
7 purchase totals =	$920.35		$992.0338	$992.04	$992.05	$992.10