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	$157.76	9.358%	$172.5232	$172.52	$172.50	$172.50
Purchase #2	$150.51	4.134%	$156.7321	$156.73	$156.75	$156.70
Purchase #3	$116.79	9.828%	$128.2681	$128.27	$128.25	$128.30
Purchase #4	$103.66	5.520%	$109.382	$109.38	$109.40	$109.40
Purchase #5	$12.58	7.467%	$13.5193	$13.52	$13.50	$13.50
Purchase #6	$191.89	9.686%	$210.4765	$210.48	$210.50	$210.50
Purchase #7	$30.73	6.595%	$32.7566	$32.76	$32.75	$32.80
7 purchase totals =	$763.92		$823.6578	$823.66	$823.65	$823.70