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	$208.82	13.702%	$237.4325	$237.43	$237.45	$237.40
Purchase #2	$189.40	12.588%	$213.2417	$213.24	$213.25	$213.20
Purchase #3	$101.67	7.821%	$109.6216	$109.62	$109.60	$109.60
Purchase #4	$39.30	8.839%	$42.7737	$42.77	$42.75	$42.80
Purchase #5	$162.49	10.312%	$179.246	$179.25	$179.25	$179.20
Purchase #6	$90.30	3.164%	$93.1571	$93.16	$93.15	$93.20
Purchase #7	$105.28	13.481%	$119.4728	$119.47	$119.45	$119.50
7 purchase totals =	$897.26		$994.9454	$994.94	$994.90	$994.90