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	$98.63	12.725%	$111.1807	$111.18	$111.20	$111.20
Purchase #2	$178.97	4.699%	$187.3798	$187.38	$187.40	$187.40
Purchase #3	$160.47	3.389%	$165.9083	$165.91	$165.90	$165.90
Purchase #4	$8.85	3.380%	$9.1491	$9.15	$9.15	$9.10
Purchase #5	$116.58	13.257%	$132.035	$132.04	$132.05	$132.00
Purchase #6	$89.33	12.599%	$100.5847	$100.58	$100.60	$100.60
Purchase #7	$185.46	6.183%	$196.927	$196.93	$196.95	$196.90
7 purchase totals =	$838.29		$903.1646	$903.17	$903.25	$903.10