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	$150.88	10.109%	$166.1325	$166.13	$166.15	$166.10
Purchase #2	$74.85	9.866%	$82.2347	$82.23	$82.25	$82.20
Purchase #3	$23.96	13.286%	$27.1433	$27.14	$27.15	$27.10
Purchase #4	$35.70	7.311%	$38.31	$38.31	$38.30	$38.30
Purchase #5	$234.96	9.854%	$258.113	$258.11	$258.10	$258.10
Purchase #6	$16.53	12.708%	$18.6306	$18.63	$18.65	$18.60
Purchase #7	$138.63	8.588%	$150.5355	$150.54	$150.55	$150.50
7 purchase totals =	$675.51		$741.0996	$741.09	$741.15	$740.90