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	$18.44	13.530%	$20.9349	$20.93	$20.95	$20.90
Purchase #2	$20.45	4.681%	$21.4073	$21.41	$21.40	$21.40
Purchase #3	$135.32	3.458%	$139.9994	$140.00	$140.00	$140.00
Purchase #4	$105.47	12.688%	$118.852	$118.85	$118.85	$118.90
Purchase #5	$57.49	10.381%	$63.458	$63.46	$63.45	$63.50
Purchase #6	$92.51	11.262%	$102.9285	$102.93	$102.95	$102.90
Purchase #7	$175.57	13.685%	$199.5968	$199.60	$199.60	$199.60
7 purchase totals =	$605.25		$667.1769	$667.18	$667.20	$667.20