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	$144.86	9.168%	$158.1408	$158.14	$158.15	$158.10
Purchase #2	$122.98	13.828%	$139.9857	$139.99	$140.00	$140.00
Purchase #3	$122.68	6.813%	$131.0382	$131.04	$131.05	$131.00
Purchase #4	$25.98	7.141%	$27.8352	$27.84	$27.85	$27.80
Purchase #5	$131.38	12.229%	$147.4465	$147.45	$147.45	$147.40
Purchase #6	$115.25	11.441%	$128.4358	$128.44	$128.45	$128.40
Purchase #7	$137.94	4.344%	$143.9321	$143.93	$143.95	$143.90
7 purchase totals =	$801.07		$876.8143	$876.83	$876.90	$876.60