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	$204.38	3.671%	$211.8828	$211.88	$211.90	$211.90
Purchase #2	$213.74	13.752%	$243.1335	$243.13	$243.15	$243.10
Purchase #3	$61.37	10.716%	$67.9464	$67.95	$67.95	$67.90
Purchase #4	$169.34	12.316%	$190.1959	$190.20	$190.20	$190.20
Purchase #5	$19.64	7.609%	$21.1344	$21.13	$21.15	$21.10
Purchase #6	$121.84	4.262%	$127.0328	$127.03	$127.05	$127.00
Purchase #7	$116.86	9.193%	$127.6029	$127.60	$127.60	$127.60
7 purchase totals =	$907.17		$988.9287	$988.92	$989.00	$988.80