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	$108.62	13.221%	$122.9807	$122.98	$123.00	$123.00
Purchase #2	$40.45	11.375%	$45.0512	$45.05	$45.05	$45.10
Purchase #3	$90.42	10.683%	$100.0796	$100.08	$100.10	$100.10
Purchase #4	$66.66	4.861%	$69.9003	$69.90	$69.90	$69.90
Purchase #5	$119.32	12.230%	$133.9128	$133.91	$133.90	$133.90
Purchase #6	$107.59	11.452%	$119.9112	$119.91	$119.90	$119.90
Purchase #7	$58.72	9.653%	$64.3882	$64.39	$64.40	$64.40
7 purchase totals =	$591.78		$656.2240	$656.22	$656.25	$656.30