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	$238.75	11.691%	$266.6623	$266.66	$266.65	$266.70
Purchase #2	$66.59	13.237%	$75.4045	$75.40	$75.40	$75.40
Purchase #3	$14.56	11.165%	$16.1856	$16.19	$16.20	$16.20
Purchase #4	$51.59	5.317%	$54.333	$54.33	$54.35	$54.30
Purchase #5	$54.77	8.669%	$59.518	$59.52	$59.50	$59.50
Purchase #6	$34.38	9.685%	$37.7097	$37.71	$37.70	$37.70
Purchase #7	$119.82	10.506%	$132.4083	$132.41	$132.40	$132.40
7 purchase totals =	$580.46		$642.2214	$642.22	$642.20	$642.20