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	$55.35	7.364%	$59.426	$59.43	$59.45	$59.40
Purchase #2	$248.65	13.449%	$282.0909	$282.09	$282.10	$282.10
Purchase #3	$56.26	9.544%	$61.6295	$61.63	$61.65	$61.60
Purchase #4	$130.82	6.558%	$139.3992	$139.40	$139.40	$139.40
Purchase #5	$42.40	3.533%	$43.898	$43.90	$43.90	$43.90
Purchase #6	$69.38	7.673%	$74.7035	$74.70	$74.70	$74.70
Purchase #7	$15.72	13.785%	$17.887	$17.89	$17.90	$17.90
7 purchase totals =	$618.58		$679.0341	$679.04	$679.10	$679.00