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	$72.56	10.768%	$80.3733	$80.37	$80.35	$80.40
Purchase #2	$91.50	13.124%	$103.5085	$103.51	$103.50	$103.50
Purchase #3	$180.89	8.668%	$196.5695	$196.57	$196.55	$196.60
Purchase #4	$80.92	10.480%	$89.4004	$89.40	$89.40	$89.40
Purchase #5	$131.41	8.128%	$142.091	$142.09	$142.10	$142.10
Purchase #6	$107.45	11.396%	$119.695	$119.70	$119.70	$119.70
Purchase #7	$194.69	8.680%	$211.5891	$211.59	$211.60	$211.60
7 purchase totals =	$859.42		$943.2268	$943.23	$943.20	$943.30