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	$107.38	10.198%	$118.3306	$118.33	$118.35	$118.30
Purchase #2	$59.70	3.666%	$61.8886	$61.89	$61.90	$61.90
Purchase #3	$169.75	5.698%	$179.4224	$179.42	$179.40	$179.40
Purchase #4	$230.47	4.610%	$241.0947	$241.09	$241.10	$241.10
Purchase #5	$66.83	8.760%	$72.6843	$72.68	$72.70	$72.70
Purchase #6	$42.41	7.599%	$45.6327	$45.63	$45.65	$45.60
Purchase #7	$131.31	7.357%	$140.9705	$140.97	$140.95	$141.00
7 purchase totals =	$807.85		$860.0238	$860.01	$860.05	$860.00