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	$33.61	12.480%	$37.8045	$37.80	$37.80	$37.80
Purchase #2	$14.32	3.698%	$14.8496	$14.85	$14.85	$14.80
Purchase #3	$104.55	3.206%	$107.9019	$107.90	$107.90	$107.90
Purchase #4	$171.51	10.435%	$189.4071	$189.41	$189.40	$189.40
Purchase #5	$206.47	7.431%	$221.8128	$221.81	$221.80	$221.80
Purchase #6	$151.87	6.345%	$161.5062	$161.51	$161.50	$161.50
Purchase #7	$117.25	8.763%	$127.5246	$127.52	$127.50	$127.50
7 purchase totals =	$799.58		$860.8067	$860.80	$860.75	$860.70