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	$100.80	11.581%	$112.4736	$112.47	$112.45	$112.50
Purchase #2	$95.63	11.487%	$106.615	$106.62	$106.60	$106.60
Purchase #3	$34.58	12.329%	$38.8434	$38.84	$38.85	$38.80
Purchase #4	$97.32	8.851%	$105.9338	$105.93	$105.95	$105.90
Purchase #5	$211.40	5.158%	$222.304	$222.30	$222.30	$222.30
Purchase #6	$88.54	13.236%	$100.2592	$100.26	$100.25	$100.30
Purchase #7	$242.39	7.606%	$260.8262	$260.83	$260.85	$260.80
7 purchase totals =	$870.66		$947.2552	$947.25	$947.25	$947.20