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	$40.67	4.578%	$42.5319	$42.53	$42.55	$42.50
Purchase #2	$147.59	13.766%	$167.9072	$167.91	$167.90	$167.90
Purchase #3	$118.82	7.275%	$127.4642	$127.46	$127.45	$127.50
Purchase #4	$78.52	8.186%	$84.9476	$84.95	$84.95	$84.90
Purchase #5	$80.38	8.448%	$87.1705	$87.17	$87.15	$87.20
Purchase #6	$177.38	9.477%	$194.1903	$194.19	$194.20	$194.20
Purchase #7	$36.46	5.265%	$38.3796	$38.38	$38.40	$38.40
7 purchase totals =	$679.82		$742.5913	$742.59	$742.60	$742.60