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	$54.89	10.744%	$60.7874	$60.79	$60.80	$60.80
Purchase #2	$131.69	11.105%	$146.3142	$146.31	$146.30	$146.30
Purchase #3	$208.79	7.727%	$224.9232	$224.92	$224.90	$224.90
Purchase #4	$18.44	10.505%	$20.3771	$20.38	$20.40	$20.40
Purchase #5	$247.38	8.161%	$267.5687	$267.57	$267.55	$267.60
Purchase #6	$18.51	5.525%	$19.5327	$19.53	$19.55	$19.50
Purchase #7	$94.77	6.517%	$100.9462	$100.95	$100.95	$100.90
7 purchase totals =	$774.47		$840.4495	$840.45	$840.45	$840.40