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	$79.89	13.752%	$90.8765	$90.88	$90.90	$90.90
Purchase #2	$144.54	4.683%	$151.3088	$151.31	$151.30	$151.30
Purchase #3	$36.93	12.472%	$41.5359	$41.54	$41.55	$41.50
Purchase #4	$128.78	12.786%	$145.2458	$145.25	$145.25	$145.20
Purchase #5	$146.57	10.297%	$161.6623	$161.66	$161.65	$161.70
Purchase #6	$104.44	6.757%	$111.497	$111.50	$111.50	$111.50
Purchase #7	$47.68	10.484%	$52.6788	$52.68	$52.70	$52.70
7 purchase totals =	$688.83		$754.8051	$754.82	$754.85	$754.80