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	$104.43	11.221%	$116.1481	$116.15	$116.15	$116.10
Purchase #2	$218.71	13.493%	$248.2205	$248.22	$248.20	$248.20
Purchase #3	$28.32	13.181%	$32.0529	$32.05	$32.05	$32.10
Purchase #4	$74.64	4.498%	$77.9973	$78.00	$78.00	$78.00
Purchase #5	$102.84	6.602%	$109.6295	$109.63	$109.65	$109.60
Purchase #6	$227.56	3.770%	$236.139	$236.14	$236.15	$236.10
Purchase #7	$81.95	4.429%	$85.5796	$85.58	$85.60	$85.60
7 purchase totals =	$838.45		$905.7669	$905.77	$905.80	$905.70