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	$39.56	7.566%	$42.5531	$42.55	$42.55	$42.60
Purchase #2	$113.60	5.554%	$119.9093	$119.91	$119.90	$119.90
Purchase #3	$13.57	5.413%	$14.3045	$14.30	$14.30	$14.30
Purchase #4	$100.25	5.159%	$105.4219	$105.42	$105.40	$105.40
Purchase #5	$80.61	12.427%	$90.6274	$90.63	$90.65	$90.60
Purchase #6	$95.81	4.860%	$100.4664	$100.47	$100.45	$100.50
Purchase #7	$126.31	5.515%	$133.276	$133.28	$133.30	$133.30
7 purchase totals =	$569.71		$606.5586	$606.56	$606.55	$606.60