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	$45.49	11.866%	$50.8878	$50.89	$50.90	$50.90
Purchase #2	$25.56	11.589%	$28.5221	$28.52	$28.50	$28.50
Purchase #3	$62.29	9.500%	$68.2076	$68.21	$68.20	$68.20
Purchase #4	$47.30	7.593%	$50.8915	$50.89	$50.90	$50.90
Purchase #5	$180.86	3.730%	$187.6061	$187.61	$187.60	$187.60
Purchase #6	$135.97	10.828%	$150.6928	$150.69	$150.70	$150.70
Purchase #7	$111.77	4.654%	$116.9718	$116.97	$116.95	$117.00
7 purchase totals =	$609.24		$653.7797	$653.78	$653.75	$653.80