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	$134.73	5.779%	$142.516	$142.52	$142.50	$142.50
Purchase #2	$131.28	12.318%	$147.4511	$147.45	$147.45	$147.50
Purchase #3	$122.42	9.571%	$134.1368	$134.14	$134.15	$134.10
Purchase #4	$161.75	11.217%	$179.8935	$179.89	$179.90	$179.90
Purchase #5	$89.93	10.195%	$99.0984	$99.10	$99.10	$99.10
Purchase #6	$56.75	8.536%	$61.5942	$61.59	$61.60	$61.60
Purchase #7	$22.81	8.287%	$24.7003	$24.70	$24.70	$24.70
7 purchase totals =	$719.67		$789.3903	$789.39	$789.40	$789.40