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	$24.37	12.638%	$27.4499	$27.45	$27.45	$27.40
Purchase #2	$49.55	12.367%	$55.6778	$55.68	$55.70	$55.70
Purchase #3	$227.65	12.282%	$255.61	$255.61	$255.60	$255.60
Purchase #4	$238.73	9.152%	$260.5786	$260.58	$260.60	$260.60
Purchase #5	$169.46	9.396%	$185.3825	$185.38	$185.40	$185.40
Purchase #6	$145.67	7.331%	$156.3491	$156.35	$156.35	$156.30
Purchase #7	$83.45	5.359%	$87.9221	$87.92	$87.90	$87.90
7 purchase totals =	$938.88		$1,028.9700	$1,028.97	$1,029.00	$1,028.90