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	$245.90	9.563%	$269.4154	$269.42	$269.40	$269.40
Purchase #2	$135.84	6.610%	$144.819	$144.82	$144.80	$144.80
Purchase #3	$241.33	4.477%	$252.1343	$252.13	$252.15	$252.10
Purchase #4	$85.55	5.341%	$90.1192	$90.12	$90.10	$90.10
Purchase #5	$74.27	10.738%	$82.2451	$82.25	$82.25	$82.20
Purchase #6	$129.50	8.473%	$140.4725	$140.47	$140.45	$140.50
Purchase #7	$185.76	3.763%	$192.7501	$192.75	$192.75	$192.80
7 purchase totals =	$1,098.15		$1,171.9556	$1,171.96	$1,171.90	$1,171.90