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	$248.25	3.204%	$256.2039	$256.20	$256.20	$256.20
Purchase #2	$206.69	10.700%	$228.8058	$228.81	$228.80	$228.80
Purchase #3	$82.43	11.239%	$91.6943	$91.69	$91.70	$91.70
Purchase #4	$189.95	12.442%	$213.5836	$213.58	$213.60	$213.60
Purchase #5	$82.50	9.246%	$90.128	$90.13	$90.15	$90.10
Purchase #6	$113.32	6.435%	$120.6121	$120.61	$120.60	$120.60
Purchase #7	$46.80	4.358%	$48.8395	$48.84	$48.85	$48.80
7 purchase totals =	$969.94		$1,049.8672	$1,049.86	$1,049.90	$1,049.80