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	$35.45	7.433%	$38.085	$38.09	$38.10	$38.10
Purchase #2	$81.37	9.345%	$88.974	$88.97	$88.95	$89.00
Purchase #3	$104.51	8.182%	$113.061	$113.06	$113.05	$113.10
Purchase #4	$133.56	13.412%	$151.4731	$151.47	$151.45	$151.50
Purchase #5	$18.89	11.659%	$21.0924	$21.09	$21.10	$21.10
Purchase #6	$243.31	9.577%	$266.6118	$266.61	$266.60	$266.60
Purchase #7	$124.85	5.613%	$131.8578	$131.86	$131.85	$131.90
7 purchase totals =	$741.94		$811.1551	$811.15	$811.10	$811.30