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	$39.52	6.790%	$42.2034	$42.20	$42.20	$42.20
Purchase #2	$8.43	11.527%	$9.4017	$9.40	$9.40	$9.40
Purchase #3	$117.57	12.636%	$132.4261	$132.43	$132.45	$132.40
Purchase #4	$154.96	6.214%	$164.5892	$164.59	$164.60	$164.60
Purchase #5	$25.84	6.820%	$27.6023	$27.60	$27.60	$27.60
Purchase #6	$42.45	7.404%	$45.593	$45.59	$45.60	$45.60
Purchase #7	$175.52	4.115%	$182.7426	$182.74	$182.75	$182.70
7 purchase totals =	$564.29		$604.5583	$604.55	$604.60	$604.50