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	$65.36	12.262%	$73.3744	$73.37	$73.35	$73.40
Purchase #2	$116.70	9.127%	$127.3512	$127.35	$127.35	$127.40
Purchase #3	$153.59	6.399%	$163.4182	$163.42	$163.40	$163.40
Purchase #4	$87.96	3.318%	$90.8785	$90.88	$90.90	$90.90
Purchase #5	$148.81	11.175%	$165.4395	$165.44	$165.45	$165.40
Purchase #6	$162.85	10.699%	$180.2733	$180.27	$180.25	$180.30
Purchase #7	$60.41	3.855%	$62.7388	$62.74	$62.75	$62.70
7 purchase totals =	$795.68		$863.4739	$863.47	$863.45	$863.50