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	$103.77	8.545%	$112.6371	$112.64	$112.65	$112.60
Purchase #2	$158.91	10.673%	$175.8705	$175.87	$175.85	$175.90
Purchase #3	$10.59	7.213%	$11.3539	$11.35	$11.35	$11.40
Purchase #4	$122.58	6.794%	$130.9081	$130.91	$130.90	$130.90
Purchase #5	$23.78	5.144%	$25.0032	$25.00	$25.00	$25.00
Purchase #6	$115.93	13.503%	$131.584	$131.58	$131.60	$131.60
Purchase #7	$59.98	4.864%	$62.8974	$62.90	$62.90	$62.90
7 purchase totals =	$595.54		$650.2542	$650.25	$650.25	$650.30