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	$69.92	7.183%	$74.9424	$74.94	$74.95	$74.90
Purchase #2	$7.33	10.775%	$8.1198	$8.12	$8.10	$8.10
Purchase #3	$151.66	10.726%	$167.9271	$167.93	$167.95	$167.90
Purchase #4	$56.50	5.709%	$59.7256	$59.73	$59.75	$59.70
Purchase #5	$85.34	6.511%	$90.8965	$90.90	$90.90	$90.90
Purchase #6	$119.44	3.583%	$123.7195	$123.72	$123.70	$123.70
Purchase #7	$101.81	12.249%	$114.2807	$114.28	$114.30	$114.30
7 purchase totals =	$592.00		$639.6116	$639.62	$639.65	$639.50