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	$36.34	11.684%	$40.586	$40.59	$40.60	$40.60
Purchase #2	$102.68	5.710%	$108.543	$108.54	$108.55	$108.50
Purchase #3	$12.95	9.449%	$14.1736	$14.17	$14.15	$14.20
Purchase #4	$157.42	9.421%	$172.2505	$172.25	$172.25	$172.30
Purchase #5	$10.95	4.421%	$11.4341	$11.43	$11.45	$11.40
Purchase #6	$89.47	7.805%	$96.4531	$96.45	$96.45	$96.50
Purchase #7	$102.92	11.348%	$114.5994	$114.60	$114.60	$114.60
7 purchase totals =	$512.73		$558.0397	$558.03	$558.05	$558.10