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	$138.90	9.347%	$151.883	$151.88	$151.90	$151.90
Purchase #2	$62.39	7.313%	$66.9526	$66.95	$66.95	$67.00
Purchase #3	$83.41	3.698%	$86.4945	$86.49	$86.50	$86.50
Purchase #4	$203.87	6.860%	$217.8555	$217.86	$217.85	$217.90
Purchase #5	$139.77	9.122%	$152.5198	$152.52	$152.50	$152.50
Purchase #6	$131.54	8.872%	$143.2102	$143.21	$143.20	$143.20
Purchase #7	$86.57	3.233%	$89.3688	$89.37	$89.35	$89.40
7 purchase totals =	$846.45		$908.2844	$908.28	$908.25	$908.40