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	$15.49	8.826%	$16.8571	$16.86	$16.85	$16.90
Purchase #2	$22.76	7.297%	$24.4208	$24.42	$24.40	$24.40
Purchase #3	$99.98	11.544%	$111.5217	$111.52	$111.50	$111.50
Purchase #4	$176.62	3.591%	$182.9624	$182.96	$182.95	$183.00
Purchase #5	$95.40	3.298%	$98.5463	$98.55	$98.55	$98.50
Purchase #6	$170.94	7.542%	$183.8323	$183.83	$183.85	$183.80
Purchase #7	$18.51	8.830%	$20.1444	$20.14	$20.15	$20.10
7 purchase totals =	$599.70		$638.2850	$638.28	$638.25	$638.20