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	$82.63	8.431%	$89.5965	$89.60	$89.60	$89.60
Purchase #2	$31.56	10.872%	$34.9912	$34.99	$35.00	$35.00
Purchase #3	$235.96	13.554%	$267.942	$267.94	$267.95	$267.90
Purchase #4	$163.91	4.642%	$171.5187	$171.52	$171.50	$171.50
Purchase #5	$214.51	7.758%	$231.1517	$231.15	$231.15	$231.20
Purchase #6	$53.92	6.578%	$57.4669	$57.47	$57.45	$57.50
Purchase #7	$78.64	5.742%	$83.1555	$83.16	$83.15	$83.20
7 purchase totals =	$861.13		$935.8225	$935.83	$935.80	$935.90