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	$13.86	6.622%	$14.7778	$14.78	$14.80	$14.80
Purchase #2	$92.44	12.359%	$103.8647	$103.86	$103.85	$103.90
Purchase #3	$16.53	10.507%	$18.2668	$18.27	$18.25	$18.30
Purchase #4	$138.91	10.182%	$153.0538	$153.05	$153.05	$153.10
Purchase #5	$20.40	8.473%	$22.1285	$22.13	$22.15	$22.10
Purchase #6	$171.76	7.453%	$184.5613	$184.56	$184.55	$184.60
Purchase #7	$196.60	13.503%	$223.1469	$223.15	$223.15	$223.10
7 purchase totals =	$650.50		$719.7998	$719.80	$719.80	$719.90