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	$237.67	7.493%	$255.4786	$255.48	$255.50	$255.50
Purchase #2	$38.47	12.139%	$43.1399	$43.14	$43.15	$43.10
Purchase #3	$51.30	8.209%	$55.5112	$55.51	$55.50	$55.50
Purchase #4	$116.84	4.847%	$122.5032	$122.50	$122.50	$122.50
Purchase #5	$32.62	5.779%	$34.5051	$34.51	$34.50	$34.50
Purchase #6	$245.77	3.372%	$254.0574	$254.06	$254.05	$254.10
Purchase #7	$224.63	6.134%	$238.4088	$238.41	$238.40	$238.40
7 purchase totals =	$947.30		$1,003.6042	$1,003.61	$1,003.60	$1,003.60