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	$119.25	3.421%	$123.3295	$123.33	$123.35	$123.30
Purchase #2	$238.39	4.359%	$248.7814	$248.78	$248.80	$248.80
Purchase #3	$147.86	8.563%	$160.5213	$160.52	$160.50	$160.50
Purchase #4	$139.66	13.585%	$158.6328	$158.63	$158.65	$158.60
Purchase #5	$186.52	11.797%	$208.5238	$208.52	$208.50	$208.50
Purchase #6	$78.30	10.870%	$86.8112	$86.81	$86.80	$86.80
Purchase #7	$50.64	3.215%	$52.2681	$52.27	$52.25	$52.30
7 purchase totals =	$960.62		$1,038.8681	$1,038.86	$1,038.85	$1,038.80