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	$117.81	4.643%	$123.2799	$123.28	$123.30	$123.30
Purchase #2	$222.98	9.427%	$244.0003	$244.00	$244.00	$244.00
Purchase #3	$114.69	3.835%	$119.0884	$119.09	$119.10	$119.10
Purchase #4	$150.90	12.580%	$169.8832	$169.88	$169.90	$169.90
Purchase #5	$49.62	10.635%	$54.8971	$54.90	$54.90	$54.90
Purchase #6	$34.83	12.702%	$39.2541	$39.25	$39.25	$39.30
Purchase #7	$156.84	9.706%	$172.0629	$172.06	$172.05	$172.10
7 purchase totals =	$847.67		$922.4659	$922.46	$922.50	$922.60