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	$117.43	10.551%	$129.82	$129.82	$129.80	$129.80
Purchase #2	$192.25	3.420%	$198.825	$198.83	$198.85	$198.80
Purchase #3	$23.63	3.551%	$24.4691	$24.47	$24.45	$24.50
Purchase #4	$134.76	11.501%	$150.2587	$150.26	$150.25	$150.30
Purchase #5	$33.93	10.438%	$37.4716	$37.47	$37.45	$37.50
Purchase #6	$134.62	11.529%	$150.1403	$150.14	$150.15	$150.10
Purchase #7	$101.55	4.224%	$105.8395	$105.84	$105.85	$105.80
7 purchase totals =	$738.17		$796.8242	$796.83	$796.80	$796.80