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	$28.65	8.523%	$31.0918	$31.09	$31.10	$31.10
Purchase #2	$190.80	7.606%	$205.3122	$205.31	$205.30	$205.30
Purchase #3	$134.31	4.503%	$140.358	$140.36	$140.35	$140.40
Purchase #4	$35.50	6.626%	$37.8522	$37.85	$37.85	$37.90
Purchase #5	$20.60	4.383%	$21.5029	$21.50	$21.50	$21.50
Purchase #6	$227.76	5.865%	$241.1181	$241.12	$241.10	$241.10
Purchase #7	$132.82	9.299%	$145.1709	$145.17	$145.15	$145.20
7 purchase totals =	$770.44		$822.4061	$822.40	$822.35	$822.50