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	$213.74	11.751%	$238.8566	$238.86	$238.85	$238.90
Purchase #2	$74.79	7.736%	$80.5758	$80.58	$80.60	$80.60
Purchase #3	$212.57	9.846%	$233.4996	$233.50	$233.50	$233.50
Purchase #4	$143.72	9.133%	$156.8459	$156.85	$156.85	$156.80
Purchase #5	$122.41	4.523%	$127.9466	$127.95	$127.95	$127.90
Purchase #6	$73.76	8.715%	$80.1882	$80.19	$80.20	$80.20
Purchase #7	$62.45	6.433%	$66.4674	$66.47	$66.45	$66.50
7 purchase totals =	$903.44		$984.3801	$984.40	$984.40	$984.40