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	$142.54	5.255%	$150.0305	$150.03	$150.05	$150.00
Purchase #2	$75.36	10.594%	$83.3436	$83.34	$83.35	$83.30
Purchase #3	$137.75	4.443%	$143.8702	$143.87	$143.85	$143.90
Purchase #4	$172.33	9.200%	$188.1844	$188.18	$188.20	$188.20
Purchase #5	$18.83	12.554%	$21.1939	$21.19	$21.20	$21.20
Purchase #6	$32.76	3.521%	$33.9135	$33.91	$33.90	$33.90
Purchase #7	$63.34	13.675%	$72.0017	$72.00	$72.00	$72.00
7 purchase totals =	$642.91		$692.5378	$692.52	$692.55	$692.50