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	$40.81	4.486%	$42.6407	$42.64	$42.65	$42.60
Purchase #2	$81.29	12.219%	$91.2228	$91.22	$91.20	$91.20
Purchase #3	$167.63	11.371%	$186.6912	$186.69	$186.70	$186.70
Purchase #4	$95.51	5.321%	$100.5921	$100.59	$100.60	$100.60
Purchase #5	$113.39	12.580%	$127.6545	$127.65	$127.65	$127.70
Purchase #6	$167.69	5.309%	$176.5927	$176.59	$176.60	$176.60
Purchase #7	$134.75	9.123%	$147.0432	$147.04	$147.05	$147.00
7 purchase totals =	$801.07		$872.4372	$872.42	$872.45	$872.40