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	$19.38	9.136%	$21.1506	$21.15	$21.15	$21.20
Purchase #2	$17.31	11.456%	$19.293	$19.29	$19.30	$19.30
Purchase #3	$201.67	3.158%	$208.0387	$208.04	$208.05	$208.00
Purchase #4	$56.54	5.691%	$59.7577	$59.76	$59.75	$59.80
Purchase #5	$120.83	10.532%	$133.5558	$133.56	$133.55	$133.60
Purchase #6	$63.87	3.823%	$66.3118	$66.31	$66.30	$66.30
Purchase #7	$51.32	6.825%	$54.8226	$54.82	$54.80	$54.80
7 purchase totals =	$530.92		$562.9302	$562.93	$562.90	$563.00