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	$82.42	10.406%	$90.9966	$91.00	$91.00	$91.00
Purchase #2	$36.71	11.137%	$40.7984	$40.80	$40.80	$40.80
Purchase #3	$172.31	7.567%	$185.3487	$185.35	$185.35	$185.30
Purchase #4	$246.32	3.625%	$255.2491	$255.25	$255.25	$255.20
Purchase #5	$208.50	3.789%	$216.4001	$216.40	$216.40	$216.40
Purchase #6	$34.49	11.493%	$38.4539	$38.45	$38.45	$38.50
Purchase #7	$95.39	12.559%	$107.37	$107.37	$107.35	$107.40
7 purchase totals =	$876.14		$934.6168	$934.62	$934.60	$934.60