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	$51.90	7.831%	$55.9643	$55.96	$55.95	$56.00
Purchase #2	$73.52	3.871%	$76.366	$76.37	$76.35	$76.40
Purchase #3	$241.57	5.706%	$255.354	$255.35	$255.35	$255.40
Purchase #4	$75.60	3.338%	$78.1235	$78.12	$78.10	$78.10
Purchase #5	$63.76	10.632%	$70.539	$70.54	$70.55	$70.50
Purchase #6	$220.59	10.593%	$243.9571	$243.96	$243.95	$244.00
Purchase #7	$52.59	13.544%	$59.7128	$59.71	$59.70	$59.70
7 purchase totals =	$779.53		$840.0167	$840.01	$839.95	$840.10