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	$50.63	5.810%	$53.5716	$53.57	$53.55	$53.60
Purchase #2	$149.46	10.351%	$164.9306	$164.93	$164.95	$164.90
Purchase #3	$140.54	8.733%	$152.8134	$152.81	$152.80	$152.80
Purchase #4	$18.27	11.416%	$20.3557	$20.36	$20.35	$20.40
Purchase #5	$144.30	12.698%	$162.6232	$162.62	$162.60	$162.60
Purchase #6	$155.41	4.264%	$162.0367	$162.04	$162.05	$162.00
Purchase #7	$144.31	8.182%	$156.1174	$156.12	$156.10	$156.10
7 purchase totals =	$802.92		$872.4486	$872.45	$872.40	$872.40