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	$127.41	6.822%	$136.1019	$136.10	$136.10	$136.10
Purchase #2	$37.91	6.460%	$40.359	$40.36	$40.35	$40.40
Purchase #3	$165.96	5.163%	$174.5285	$174.53	$174.55	$174.50
Purchase #4	$151.53	6.563%	$161.4749	$161.47	$161.45	$161.50
Purchase #5	$102.42	9.249%	$111.8928	$111.89	$111.90	$111.90
Purchase #6	$158.88	5.382%	$167.4309	$167.43	$167.45	$167.40
Purchase #7	$22.98	3.471%	$23.7776	$23.78	$23.80	$23.80
7 purchase totals =	$767.09		$815.5656	$815.56	$815.60	$815.60