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	$15.87	11.681%	$17.7238	$17.72	$17.70	$17.70
Purchase #2	$23.94	4.361%	$24.984	$24.98	$25.00	$25.00
Purchase #3	$241.61	7.172%	$258.9383	$258.94	$258.95	$258.90
Purchase #4	$227.71	12.371%	$255.88	$255.88	$255.90	$255.90
Purchase #5	$66.48	8.566%	$72.1747	$72.17	$72.15	$72.20
Purchase #6	$203.73	8.637%	$221.3262	$221.33	$221.35	$221.30
Purchase #7	$112.66	13.203%	$127.5345	$127.53	$127.55	$127.50
7 purchase totals =	$892.00		$978.5615	$978.55	$978.60	$978.50