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	$82.82	8.719%	$90.0411	$90.04	$90.05	$90.00
Purchase #2	$58.65	13.592%	$66.6217	$66.62	$66.60	$66.60
Purchase #3	$165.94	13.309%	$188.025	$188.03	$188.05	$188.00
Purchase #4	$26.42	4.763%	$27.6784	$27.68	$27.70	$27.70
Purchase #5	$69.45	3.690%	$72.0127	$72.01	$72.00	$72.00
Purchase #6	$166.37	3.647%	$172.4375	$172.44	$172.45	$172.40
Purchase #7	$178.92	3.386%	$184.9782	$184.98	$185.00	$185.00
7 purchase totals =	$748.57		$801.7946	$801.80	$801.85	$801.70