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	$84.27	8.599%	$91.5164	$91.52	$91.50	$91.50
Purchase #2	$163.60	13.650%	$185.9314	$185.93	$185.95	$185.90
Purchase #3	$107.92	10.348%	$119.0876	$119.09	$119.10	$119.10
Purchase #4	$60.33	8.821%	$65.6517	$65.65	$65.65	$65.70
Purchase #5	$89.30	12.789%	$100.7206	$100.72	$100.70	$100.70
Purchase #6	$125.85	11.309%	$140.0824	$140.08	$140.10	$140.10
Purchase #7	$158.45	3.685%	$164.2889	$164.29	$164.30	$164.30
7 purchase totals =	$789.72		$867.2790	$867.28	$867.30	$867.30