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	$38.76	12.718%	$43.6895	$43.69	$43.70	$43.70
Purchase #2	$110.89	6.296%	$117.8716	$117.87	$117.85	$117.90
Purchase #3	$123.82	5.199%	$130.2574	$130.26	$130.25	$130.30
Purchase #4	$62.34	12.462%	$70.1088	$70.11	$70.10	$70.10
Purchase #5	$145.87	9.329%	$159.4782	$159.48	$159.50	$159.50
Purchase #6	$166.74	11.856%	$186.5087	$186.51	$186.50	$186.50
Purchase #7	$12.81	5.135%	$13.4678	$13.47	$13.45	$13.50
7 purchase totals =	$661.23		$721.3820	$721.39	$721.35	$721.50