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	$220.52	8.119%	$238.424	$238.42	$238.40	$238.40
Purchase #2	$140.89	3.561%	$145.9071	$145.91	$145.90	$145.90
Purchase #3	$35.68	12.376%	$40.0958	$40.10	$40.10	$40.10
Purchase #4	$85.82	13.378%	$97.301	$97.30	$97.30	$97.30
Purchase #5	$174.53	9.114%	$190.4367	$190.44	$190.45	$190.40
Purchase #6	$208.28	13.790%	$237.0018	$237.00	$237.00	$237.00
Purchase #7	$208.71	10.849%	$231.3529	$231.35	$231.35	$231.40
7 purchase totals =	$1,074.43		$1,180.5193	$1,180.52	$1,180.50	$1,180.50