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	$145.59	10.263%	$160.5319	$160.53	$160.55	$160.50
Purchase #2	$34.40	11.720%	$38.4317	$38.43	$38.45	$38.40
Purchase #3	$95.83	9.868%	$105.2865	$105.29	$105.30	$105.30
Purchase #4	$87.60	5.649%	$92.5485	$92.55	$92.55	$92.50
Purchase #5	$18.63	11.297%	$20.7346	$20.73	$20.75	$20.70
Purchase #6	$15.73	9.461%	$17.2182	$17.22	$17.20	$17.20
Purchase #7	$82.95	4.639%	$86.7981	$86.80	$86.80	$86.80
7 purchase totals =	$480.73		$521.5495	$521.55	$521.60	$521.40