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	$106.25	3.452%	$109.9178	$109.92	$109.90	$109.90
Purchase #2	$131.52	12.177%	$147.5352	$147.54	$147.55	$147.50
Purchase #3	$43.50	10.514%	$48.0736	$48.07	$48.05	$48.10
Purchase #4	$55.44	7.143%	$59.4001	$59.40	$59.40	$59.40
Purchase #5	$230.85	4.514%	$241.2706	$241.27	$241.25	$241.30
Purchase #6	$59.39	5.315%	$62.5466	$62.55	$62.55	$62.50
Purchase #7	$117.34	12.599%	$132.1237	$132.12	$132.10	$132.10
7 purchase totals =	$744.29		$800.8676	$800.87	$800.80	$800.80