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	$237.54	8.142%	$256.8805	$256.88	$256.90	$256.90
Purchase #2	$43.74	3.411%	$45.232	$45.23	$45.25	$45.20
Purchase #3	$49.66	12.489%	$55.862	$55.86	$55.85	$55.90
Purchase #4	$145.38	5.526%	$153.4137	$153.41	$153.40	$153.40
Purchase #5	$146.56	6.626%	$156.2711	$156.27	$156.25	$156.30
Purchase #6	$151.72	11.835%	$169.6761	$169.68	$169.70	$169.70
Purchase #7	$147.73	4.803%	$154.8255	$154.83	$154.85	$154.80
7 purchase totals =	$922.33		$992.1609	$992.16	$992.20	$992.20