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	$161.30	11.314%	$179.5495	$179.55	$179.55	$179.50
Purchase #2	$139.27	4.405%	$145.4048	$145.40	$145.40	$145.40
Purchase #3	$178.32	12.442%	$200.5066	$200.51	$200.50	$200.50
Purchase #4	$156.66	8.674%	$170.2487	$170.25	$170.25	$170.20
Purchase #5	$22.96	10.819%	$25.444	$25.44	$25.45	$25.40
Purchase #6	$145.39	5.554%	$153.465	$153.47	$153.45	$153.50
Purchase #7	$105.60	11.339%	$117.574	$117.57	$117.55	$117.60
7 purchase totals =	$909.50		$992.1926	$992.19	$992.15	$992.10