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	$119.51	12.828%	$134.8407	$134.84	$134.85	$134.80
Purchase #2	$30.25	6.806%	$32.3088	$32.31	$32.30	$32.30
Purchase #3	$136.60	8.257%	$147.8791	$147.88	$147.90	$147.90
Purchase #4	$137.44	3.458%	$142.1927	$142.19	$142.20	$142.20
Purchase #5	$105.44	13.462%	$119.6343	$119.63	$119.65	$119.60
Purchase #6	$178.77	6.684%	$190.719	$190.72	$190.70	$190.70
Purchase #7	$38.89	3.762%	$40.353	$40.35	$40.35	$40.40
7 purchase totals =	$746.90		$807.9276	$807.92	$807.95	$807.90