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	$121.73	12.794%	$137.3041	$137.30	$137.30	$137.30
Purchase #2	$60.88	4.848%	$63.8315	$63.83	$63.85	$63.80
Purchase #3	$21.80	3.312%	$22.522	$22.52	$22.50	$22.50
Purchase #4	$166.35	11.379%	$185.279	$185.28	$185.30	$185.30
Purchase #5	$37.56	7.841%	$40.5051	$40.51	$40.50	$40.50
Purchase #6	$181.78	9.247%	$198.5892	$198.59	$198.60	$198.60
Purchase #7	$101.64	11.612%	$113.4424	$113.44	$113.45	$113.40
7 purchase totals =	$691.74		$761.4733	$761.47	$761.50	$761.40