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	$214.79	11.421%	$239.3212	$239.32	$239.30	$239.30
Purchase #2	$42.47	13.695%	$48.2863	$48.29	$48.30	$48.30
Purchase #3	$210.85	9.125%	$230.0901	$230.09	$230.10	$230.10
Purchase #4	$37.71	12.539%	$42.4385	$42.44	$42.45	$42.40
Purchase #5	$96.35	6.780%	$102.8825	$102.88	$102.90	$102.90
Purchase #6	$84.78	6.851%	$90.5883	$90.59	$90.60	$90.60
Purchase #7	$71.55	9.253%	$78.1705	$78.17	$78.15	$78.20
7 purchase totals =	$758.50		$831.7774	$831.78	$831.80	$831.80