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	$123.63	12.174%	$138.6807	$138.68	$138.70	$138.70
Purchase #2	$178.26	8.588%	$193.569	$193.57	$193.55	$193.60
Purchase #3	$18.31	10.441%	$20.2217	$20.22	$20.20	$20.20
Purchase #4	$103.68	7.128%	$111.0703	$111.07	$111.05	$111.10
Purchase #5	$111.51	9.211%	$121.7812	$121.78	$121.80	$121.80
Purchase #6	$154.47	6.464%	$164.4549	$164.45	$164.45	$164.50
Purchase #7	$33.30	11.258%	$37.0489	$37.05	$37.05	$37.00
7 purchase totals =	$723.16		$786.8267	$786.82	$786.80	$786.90