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	$225.69	13.373%	$255.8715	$255.87	$255.85	$255.90
Purchase #2	$31.36	7.766%	$33.7954	$33.80	$33.80	$33.80
Purchase #3	$39.25	10.237%	$43.268	$43.27	$43.25	$43.30
Purchase #4	$158.97	7.325%	$170.6146	$170.61	$170.60	$170.60
Purchase #5	$160.72	7.287%	$172.4317	$172.43	$172.45	$172.40
Purchase #6	$242.61	12.807%	$273.6811	$273.68	$273.70	$273.70
Purchase #7	$53.50	9.489%	$58.5766	$58.58	$58.60	$58.60
7 purchase totals =	$912.10		$1,008.2389	$1,008.24	$1,008.25	$1,008.30