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	$102.33	8.848%	$111.3842	$111.38	$111.40	$111.40
Purchase #2	$151.33	6.203%	$160.717	$160.72	$160.70	$160.70
Purchase #3	$167.94	13.689%	$190.9293	$190.93	$190.95	$190.90
Purchase #4	$180.78	7.774%	$194.8338	$194.83	$194.85	$194.80
Purchase #5	$13.74	8.379%	$14.8913	$14.89	$14.90	$14.90
Purchase #6	$38.65	5.754%	$40.8739	$40.87	$40.85	$40.90
Purchase #7	$183.52	6.221%	$194.9368	$194.94	$194.95	$194.90
7 purchase totals =	$838.29		$908.5663	$908.56	$908.60	$908.50