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	$155.38	13.597%	$176.507	$176.51	$176.50	$176.50
Purchase #2	$113.71	5.281%	$119.715	$119.72	$119.70	$119.70
Purchase #3	$183.89	13.467%	$208.6545	$208.65	$208.65	$208.70
Purchase #4	$228.90	9.620%	$250.9202	$250.92	$250.90	$250.90
Purchase #5	$31.62	13.609%	$35.9232	$35.92	$35.90	$35.90
Purchase #6	$35.48	11.681%	$39.6244	$39.62	$39.60	$39.60
Purchase #7	$250.29	7.286%	$268.5261	$268.53	$268.55	$268.50
7 purchase totals =	$999.27		$1,099.8704	$1,099.87	$1,099.80	$1,099.80