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	$136.31	13.783%	$155.0976	$155.10	$155.10	$155.10
Purchase #2	$103.75	4.387%	$108.3015	$108.30	$108.30	$108.30
Purchase #3	$87.78	6.414%	$93.4102	$93.41	$93.40	$93.40
Purchase #4	$115.80	13.300%	$131.2014	$131.20	$131.20	$131.20
Purchase #5	$37.45	13.168%	$42.3814	$42.38	$42.40	$42.40
Purchase #6	$153.71	3.370%	$158.89	$158.89	$158.90	$158.90
Purchase #7	$34.96	10.731%	$38.7116	$38.71	$38.70	$38.70
7 purchase totals =	$669.76		$727.9937	$727.99	$728.00	$728.00