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	$244.62	13.659%	$278.0326	$278.03	$278.05	$278.00
Purchase #2	$160.43	9.836%	$176.2099	$176.21	$176.20	$176.20
Purchase #3	$77.91	3.120%	$80.3408	$80.34	$80.35	$80.30
Purchase #4	$142.61	6.789%	$152.2918	$152.29	$152.30	$152.30
Purchase #5	$149.35	12.209%	$167.5841	$167.58	$167.60	$167.60
Purchase #6	$48.27	13.468%	$54.771	$54.77	$54.75	$54.80
Purchase #7	$105.80	3.604%	$109.613	$109.61	$109.60	$109.60
7 purchase totals =	$928.99		$1,018.8432	$1,018.83	$1,018.85	$1,018.80