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	$38.54	9.639%	$42.2549	$42.25	$42.25	$42.30
Purchase #2	$111.48	12.341%	$125.2377	$125.24	$125.25	$125.20
Purchase #3	$52.60	13.713%	$59.813	$59.81	$59.80	$59.80
Purchase #4	$231.95	4.509%	$242.4086	$242.41	$242.40	$242.40
Purchase #5	$44.99	12.127%	$50.4459	$50.45	$50.45	$50.40
Purchase #6	$95.30	10.723%	$105.519	$105.52	$105.50	$105.50
Purchase #7	$140.93	7.695%	$151.7746	$151.77	$151.75	$151.80
7 purchase totals =	$715.79		$777.4537	$777.45	$777.40	$777.40