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	$104.90	12.805%	$118.3324	$118.33	$118.35	$118.30
Purchase #2	$69.74	12.131%	$78.2002	$78.20	$78.20	$78.20
Purchase #3	$70.59	8.788%	$76.7934	$76.79	$76.80	$76.80
Purchase #4	$22.86	12.525%	$25.7232	$25.72	$25.70	$25.70
Purchase #5	$157.43	5.602%	$166.2492	$166.25	$166.25	$166.20
Purchase #6	$155.46	10.570%	$171.8921	$171.89	$171.90	$171.90
Purchase #7	$37.95	6.409%	$40.3822	$40.38	$40.40	$40.40
7 purchase totals =	$618.93		$677.5727	$677.56	$677.60	$677.50