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	$35.95	7.295%	$38.5726	$38.57	$38.55	$38.60
Purchase #2	$43.48	11.387%	$48.4311	$48.43	$48.45	$48.40
Purchase #3	$137.98	10.194%	$152.0457	$152.05	$152.05	$152.00
Purchase #4	$221.66	5.326%	$233.4656	$233.47	$233.45	$233.50
Purchase #5	$49.83	8.641%	$54.1358	$54.14	$54.15	$54.10
Purchase #6	$184.87	3.273%	$190.9208	$190.92	$190.90	$190.90
Purchase #7	$127.35	8.872%	$138.6485	$138.65	$138.65	$138.60
7 purchase totals =	$801.12		$856.2201	$856.23	$856.20	$856.10