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	$39.89	13.261%	$45.1798	$45.18	$45.20	$45.20
Purchase #2	$49.63	9.573%	$54.3811	$54.38	$54.40	$54.40
Purchase #3	$248.84	9.232%	$271.8129	$271.81	$271.80	$271.80
Purchase #4	$156.96	4.103%	$163.4001	$163.40	$163.40	$163.40
Purchase #5	$188.31	4.495%	$196.7745	$196.77	$196.75	$196.80
Purchase #6	$42.74	8.746%	$46.478	$46.48	$46.50	$46.50
Purchase #7	$174.33	10.407%	$192.4725	$192.47	$192.45	$192.50
7 purchase totals =	$900.70		$970.4989	$970.49	$970.50	$970.60