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	$31.58	9.521%	$34.5867	$34.59	$34.60	$34.60
Purchase #2	$212.72	13.658%	$241.7733	$241.77	$241.75	$241.80
Purchase #3	$41.77	13.534%	$47.4232	$47.42	$47.40	$47.40
Purchase #4	$150.60	3.319%	$155.5984	$155.60	$155.60	$155.60
Purchase #5	$78.96	4.496%	$82.51	$82.51	$82.50	$82.50
Purchase #6	$213.52	12.872%	$241.0043	$241.00	$241.00	$241.00
Purchase #7	$162.34	10.170%	$178.85	$178.85	$178.85	$178.90
7 purchase totals =	$891.49		$981.7459	$981.74	$981.70	$981.80