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	$134.52	3.387%	$139.0762	$139.08	$139.10	$139.10
Purchase #2	$16.92	10.189%	$18.644	$18.64	$18.65	$18.60
Purchase #3	$162.62	6.455%	$173.1171	$173.12	$173.10	$173.10
Purchase #4	$166.63	10.612%	$184.3128	$184.31	$184.30	$184.30
Purchase #5	$179.72	5.706%	$189.9748	$189.97	$189.95	$190.00
Purchase #6	$178.40	6.528%	$190.046	$190.05	$190.05	$190.00
Purchase #7	$19.83	4.475%	$20.7174	$20.72	$20.70	$20.70
7 purchase totals =	$858.64		$915.8883	$915.89	$915.85	$915.80