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	$7.93	4.229%	$8.2654	$8.27	$8.25	$8.30
Purchase #2	$93.84	9.845%	$103.0785	$103.08	$103.10	$103.10
Purchase #3	$39.87	12.250%	$44.7541	$44.75	$44.75	$44.80
Purchase #4	$183.56	3.647%	$190.2544	$190.25	$190.25	$190.30
Purchase #5	$145.88	3.658%	$151.2163	$151.22	$151.20	$151.20
Purchase #6	$47.89	10.723%	$53.0252	$53.03	$53.05	$53.00
Purchase #7	$109.87	6.293%	$116.7841	$116.78	$116.80	$116.80
7 purchase totals =	$628.84		$667.3780	$667.38	$667.40	$667.50