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	$35.82	3.838%	$37.1948	$37.19	$37.20	$37.20
Purchase #2	$56.40	6.141%	$59.8635	$59.86	$59.85	$59.90
Purchase #3	$127.57	12.461%	$143.4665	$143.47	$143.45	$143.50
Purchase #4	$146.90	9.779%	$161.2654	$161.27	$161.25	$161.30
Purchase #5	$14.54	7.187%	$15.585	$15.59	$15.60	$15.60
Purchase #6	$240.60	5.253%	$253.2387	$253.24	$253.25	$253.20
Purchase #7	$225.26	6.640%	$240.2173	$240.22	$240.20	$240.20
7 purchase totals =	$847.09		$910.8312	$910.84	$910.80	$910.90