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	$250.71	13.457%	$284.448	$284.45	$284.45	$284.40
Purchase #2	$206.97	7.394%	$222.2734	$222.27	$222.25	$222.30
Purchase #3	$116.70	5.706%	$123.3589	$123.36	$123.35	$123.40
Purchase #4	$118.45	7.675%	$127.541	$127.54	$127.55	$127.50
Purchase #5	$30.67	6.826%	$32.7635	$32.76	$32.75	$32.80
Purchase #6	$104.38	3.281%	$107.8047	$107.80	$107.80	$107.80
Purchase #7	$41.41	9.172%	$45.2081	$45.21	$45.20	$45.20
7 purchase totals =	$869.29		$943.3976	$943.39	$943.35	$943.40