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	$187.38	6.569%	$199.689	$199.69	$199.70	$199.70
Purchase #2	$147.78	3.653%	$153.1784	$153.18	$153.20	$153.20
Purchase #3	$155.92	12.276%	$175.0607	$175.06	$175.05	$175.10
Purchase #4	$132.34	5.143%	$139.1462	$139.15	$139.15	$139.10
Purchase #5	$40.77	10.520%	$45.059	$45.06	$45.05	$45.10
Purchase #6	$84.94	5.817%	$89.881	$89.88	$89.90	$89.90
Purchase #7	$61.45	7.845%	$66.2708	$66.27	$66.25	$66.30
7 purchase totals =	$810.58		$868.2851	$868.29	$868.30	$868.40