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	$120.68	13.311%	$136.7437	$136.74	$136.75	$136.70
Purchase #2	$178.25	12.531%	$200.5865	$200.59	$200.60	$200.60
Purchase #3	$137.85	6.749%	$147.1535	$147.15	$147.15	$147.20
Purchase #4	$111.82	11.182%	$124.3237	$124.32	$124.30	$124.30
Purchase #5	$201.92	7.458%	$216.9792	$216.98	$217.00	$217.00
Purchase #6	$158.59	9.373%	$173.4546	$173.45	$173.45	$173.50
Purchase #7	$28.46	9.456%	$31.1512	$31.15	$31.15	$31.20
7 purchase totals =	$937.57		$1,030.3924	$1,030.38	$1,030.40	$1,030.50