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	$134.88	6.334%	$143.4233	$143.42	$143.40	$143.40
Purchase #2	$124.90	5.382%	$131.6221	$131.62	$131.60	$131.60
Purchase #3	$145.45	12.322%	$163.3723	$163.37	$163.35	$163.40
Purchase #4	$140.51	9.382%	$153.6926	$153.69	$153.70	$153.70
Purchase #5	$209.55	5.712%	$221.5195	$221.52	$221.50	$221.50
Purchase #6	$122.90	3.458%	$127.1499	$127.15	$127.15	$127.10
Purchase #7	$150.99	11.722%	$168.689	$168.69	$168.70	$168.70
7 purchase totals =	$1,029.18		$1,109.4687	$1,109.46	$1,109.40	$1,109.40