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	$52.50	10.131%	$57.8188	$57.82	$57.80	$57.80
Purchase #2	$33.37	13.395%	$37.8399	$37.84	$37.85	$37.80
Purchase #3	$160.49	11.732%	$179.3187	$179.32	$179.30	$179.30
Purchase #4	$103.76	5.359%	$109.3205	$109.32	$109.30	$109.30
Purchase #5	$133.70	13.227%	$151.3845	$151.38	$151.40	$151.40
Purchase #6	$65.86	4.770%	$69.0015	$69.00	$69.00	$69.00
Purchase #7	$146.79	4.589%	$153.5262	$153.53	$153.55	$153.50
7 purchase totals =	$696.47		$758.2101	$758.21	$758.20	$758.10