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	$158.65	6.607%	$169.132	$169.13	$169.15	$169.10
Purchase #2	$98.79	9.840%	$108.5109	$108.51	$108.50	$108.50
Purchase #3	$29.90	4.246%	$31.1696	$31.17	$31.15	$31.20
Purchase #4	$236.60	5.283%	$249.0996	$249.10	$249.10	$249.10
Purchase #5	$88.26	12.697%	$99.4664	$99.47	$99.45	$99.50
Purchase #6	$221.43	4.359%	$231.0821	$231.08	$231.10	$231.10
Purchase #7	$99.60	5.385%	$104.9635	$104.96	$104.95	$105.00
7 purchase totals =	$933.23		$993.4241	$993.42	$993.40	$993.50