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	$24.68	9.325%	$26.9814	$26.98	$27.00	$27.00
Purchase #2	$81.37	11.637%	$90.839	$90.84	$90.85	$90.80
Purchase #3	$249.87	12.121%	$280.1567	$280.16	$280.15	$280.20
Purchase #4	$40.94	10.175%	$45.1056	$45.11	$45.10	$45.10
Purchase #5	$224.32	13.670%	$254.9845	$254.98	$255.00	$255.00
Purchase #6	$246.35	7.770%	$265.4914	$265.49	$265.50	$265.50
Purchase #7	$66.30	7.389%	$71.1989	$71.20	$71.20	$71.20
7 purchase totals =	$933.83		$1,034.7575	$1,034.76	$1,034.80	$1,034.80