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	$20.41	4.270%	$21.2815	$21.28	$21.30	$21.30
Purchase #2	$37.41	5.787%	$39.5749	$39.57	$39.55	$39.60
Purchase #3	$247.57	13.426%	$280.8087	$280.81	$280.80	$280.80
Purchase #4	$233.43	5.635%	$246.5838	$246.58	$246.60	$246.60
Purchase #5	$163.45	8.445%	$177.2534	$177.25	$177.25	$177.30
Purchase #6	$72.71	8.463%	$78.8634	$78.86	$78.85	$78.90
Purchase #7	$227.49	3.652%	$235.7979	$235.80	$235.80	$235.80
7 purchase totals =	$1,002.47		$1,080.1636	$1,080.15	$1,080.15	$1,080.30