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	$15.70	9.333%	$17.1653	$17.17	$17.15	$17.20
Purchase #2	$221.44	3.778%	$229.806	$229.81	$229.80	$229.80
Purchase #3	$156.78	5.630%	$165.6067	$165.61	$165.60	$165.60
Purchase #4	$43.28	12.840%	$48.8372	$48.84	$48.85	$48.80
Purchase #5	$9.46	12.351%	$10.6284	$10.63	$10.65	$10.60
Purchase #6	$152.57	12.767%	$172.0486	$172.05	$172.05	$172.00
Purchase #7	$111.41	11.230%	$123.9213	$123.92	$123.90	$123.90
7 purchase totals =	$710.64		$768.0135	$768.03	$768.00	$767.90