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	$19.56	12.677%	$22.0396	$22.04	$22.05	$22.00
Purchase #2	$118.38	4.124%	$123.262	$123.26	$123.25	$123.30
Purchase #3	$44.42	11.685%	$49.6105	$49.61	$49.60	$49.60
Purchase #4	$171.70	10.812%	$190.2642	$190.26	$190.25	$190.30
Purchase #5	$124.56	11.122%	$138.4136	$138.41	$138.40	$138.40
Purchase #6	$25.98	4.749%	$27.2138	$27.21	$27.20	$27.20
Purchase #7	$99.28	12.258%	$111.4497	$111.45	$111.45	$111.40
7 purchase totals =	$603.88		$662.2534	$662.24	$662.20	$662.20