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	$78.76	13.785%	$89.6171	$89.62	$89.60	$89.60
Purchase #2	$73.35	11.480%	$81.7706	$81.77	$81.75	$81.80
Purchase #3	$60.88	9.773%	$66.8298	$66.83	$66.85	$66.80
Purchase #4	$47.62	4.144%	$49.5934	$49.59	$49.60	$49.60
Purchase #5	$130.32	5.388%	$137.3416	$137.34	$137.35	$137.30
Purchase #6	$178.65	10.786%	$197.9192	$197.92	$197.90	$197.90
Purchase #7	$49.49	8.857%	$53.8733	$53.87	$53.85	$53.90
7 purchase totals =	$619.07		$676.9450	$676.94	$676.90	$676.90