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	$35.53	7.775%	$38.2925	$38.29	$38.30	$38.30
Purchase #2	$48.59	13.697%	$55.2454	$55.25	$55.25	$55.20
Purchase #3	$158.40	4.108%	$164.9071	$164.91	$164.90	$164.90
Purchase #4	$86.56	3.773%	$89.8259	$89.83	$89.85	$89.80
Purchase #5	$62.36	6.157%	$66.1995	$66.20	$66.20	$66.20
Purchase #6	$82.28	9.429%	$90.0382	$90.04	$90.05	$90.00
Purchase #7	$153.70	11.493%	$171.3647	$171.36	$171.35	$171.40
7 purchase totals =	$627.42		$675.8733	$675.88	$675.90	$675.80