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	$150.88	12.141%	$169.1983	$169.20	$169.20	$169.20
Purchase #2	$197.71	10.191%	$217.8586	$217.86	$217.85	$217.90
Purchase #3	$75.39	3.788%	$78.2458	$78.25	$78.25	$78.20
Purchase #4	$214.45	3.759%	$222.5112	$222.51	$222.50	$222.50
Purchase #5	$106.30	7.834%	$114.6275	$114.63	$114.65	$114.60
Purchase #6	$11.75	11.162%	$13.0615	$13.06	$13.05	$13.10
Purchase #7	$244.29	7.296%	$262.1134	$262.11	$262.10	$262.10
7 purchase totals =	$1,000.77		$1,077.6163	$1,077.62	$1,077.60	$1,077.60