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	$52.99	11.346%	$59.0022	$59.00	$59.00	$59.00
Purchase #2	$156.43	10.253%	$172.4688	$172.47	$172.45	$172.50
Purchase #3	$40.73	9.687%	$44.6755	$44.68	$44.70	$44.70
Purchase #4	$176.58	7.312%	$189.4915	$189.49	$189.50	$189.50
Purchase #5	$18.92	8.517%	$20.5314	$20.53	$20.55	$20.50
Purchase #6	$31.32	7.510%	$33.6721	$33.67	$33.65	$33.70
Purchase #7	$121.80	5.777%	$128.8364	$128.84	$128.85	$128.80
7 purchase totals =	$598.77		$648.6779	$648.68	$648.70	$648.70