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	$140.64	3.464%	$145.5118	$145.51	$145.50	$145.50
Purchase #2	$138.97	9.296%	$151.8887	$151.89	$151.90	$151.90
Purchase #3	$237.77	8.849%	$258.8103	$258.81	$258.80	$258.80
Purchase #4	$76.61	12.582%	$86.2491	$86.25	$86.25	$86.20
Purchase #5	$124.90	12.444%	$140.4426	$140.44	$140.45	$140.40
Purchase #6	$98.33	11.719%	$109.8533	$109.85	$109.85	$109.90
Purchase #7	$215.95	5.859%	$228.6025	$228.60	$228.60	$228.60
7 purchase totals =	$1,033.17		$1,121.3583	$1,121.35	$1,121.35	$1,121.30