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	$100.58	3.197%	$103.7955	$103.80	$103.80	$103.80
Purchase #2	$229.45	6.756%	$244.9516	$244.95	$244.95	$245.00
Purchase #3	$152.27	6.665%	$162.4188	$162.42	$162.40	$162.40
Purchase #4	$9.83	7.476%	$10.5649	$10.56	$10.55	$10.60
Purchase #5	$19.45	9.486%	$21.295	$21.30	$21.30	$21.30
Purchase #6	$136.83	5.215%	$143.9657	$143.97	$143.95	$144.00
Purchase #7	$95.62	13.484%	$108.5134	$108.51	$108.50	$108.50
7 purchase totals =	$744.03		$795.5049	$795.51	$795.45	$795.60