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	$134.39	13.175%	$152.0959	$152.10	$152.10	$152.10
Purchase #2	$62.41	9.767%	$68.5056	$68.51	$68.50	$68.50
Purchase #3	$122.94	11.339%	$136.8802	$136.88	$136.90	$136.90
Purchase #4	$241.86	12.316%	$271.6475	$271.65	$271.65	$271.60
Purchase #5	$19.62	10.163%	$21.614	$21.61	$21.60	$21.60
Purchase #6	$66.89	7.521%	$71.9208	$71.92	$71.90	$71.90
Purchase #7	$11.89	3.116%	$12.2605	$12.26	$12.25	$12.30
7 purchase totals =	$660.00		$734.9245	$734.93	$734.90	$734.90