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	$118.92	13.155%	$134.5639	$134.56	$134.55	$134.60
Purchase #2	$115.53	10.736%	$127.9333	$127.93	$127.95	$127.90
Purchase #3	$40.40	11.265%	$44.9511	$44.95	$44.95	$45.00
Purchase #4	$163.92	12.667%	$184.6837	$184.68	$184.70	$184.70
Purchase #5	$81.36	11.719%	$90.8946	$90.89	$90.90	$90.90
Purchase #6	$80.40	12.137%	$90.1581	$90.16	$90.15	$90.20
Purchase #7	$154.45	7.510%	$166.0492	$166.05	$166.05	$166.00
7 purchase totals =	$754.98		$839.2339	$839.22	$839.25	$839.30