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	$80.64	6.270%	$85.6961	$85.70	$85.70	$85.70
Purchase #2	$35.33	8.691%	$38.4005	$38.40	$38.40	$38.40
Purchase #3	$56.54	6.865%	$60.4215	$60.42	$60.40	$60.40
Purchase #4	$202.38	12.569%	$227.8171	$227.82	$227.80	$227.80
Purchase #5	$204.61	12.661%	$230.5157	$230.52	$230.50	$230.50
Purchase #6	$119.39	3.709%	$123.8182	$123.82	$123.80	$123.80
Purchase #7	$105.92	10.469%	$117.0088	$117.01	$117.00	$117.00
7 purchase totals =	$804.81		$883.6779	$883.69	$883.60	$883.60