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	$120.40	9.592%	$131.9488	$131.95	$131.95	$131.90
Purchase #2	$149.71	10.150%	$164.9056	$164.91	$164.90	$164.90
Purchase #3	$29.60	12.656%	$33.3462	$33.35	$33.35	$33.30
Purchase #4	$163.33	8.741%	$177.6067	$177.61	$177.60	$177.60
Purchase #5	$120.45	9.518%	$131.9144	$131.91	$131.90	$131.90
Purchase #6	$230.68	4.670%	$241.4528	$241.45	$241.45	$241.50
Purchase #7	$85.99	10.141%	$94.7102	$94.71	$94.70	$94.70
7 purchase totals =	$900.16		$975.8847	$975.89	$975.85	$975.80