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	$28.98	7.213%	$31.0703	$31.07	$31.05	$31.10
Purchase #2	$11.48	9.628%	$12.5853	$12.59	$12.60	$12.60
Purchase #3	$143.83	3.189%	$148.4167	$148.42	$148.40	$148.40
Purchase #4	$137.28	7.408%	$147.4497	$147.45	$147.45	$147.40
Purchase #5	$40.30	13.192%	$45.6164	$45.62	$45.60	$45.60
Purchase #6	$154.96	7.706%	$166.9012	$166.90	$166.90	$166.90
Purchase #7	$55.31	5.121%	$58.1424	$58.14	$58.15	$58.10
7 purchase totals =	$572.14		$610.1820	$610.19	$610.15	$610.10