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	$38.80	10.270%	$42.7848	$42.78	$42.80	$42.80
Purchase #2	$163.87	5.433%	$172.7731	$172.77	$172.75	$172.80
Purchase #3	$80.65	13.127%	$91.2369	$91.24	$91.25	$91.20
Purchase #4	$130.60	10.786%	$144.6865	$144.69	$144.70	$144.70
Purchase #5	$40.32	13.468%	$45.7503	$45.75	$45.75	$45.80
Purchase #6	$138.61	13.383%	$157.1602	$157.16	$157.15	$157.20
Purchase #7	$109.87	10.590%	$121.5052	$121.51	$121.50	$121.50
7 purchase totals =	$702.72		$775.8970	$775.90	$775.90	$776.00