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	$128.26	8.311%	$138.9197	$138.92	$138.90	$138.90
Purchase #2	$230.32	13.726%	$261.9337	$261.93	$261.95	$261.90
Purchase #3	$129.86	8.550%	$140.963	$140.96	$140.95	$141.00
Purchase #4	$174.87	5.810%	$185.0299	$185.03	$185.05	$185.00
Purchase #5	$95.77	5.190%	$100.7405	$100.74	$100.75	$100.70
Purchase #6	$172.95	7.341%	$185.6463	$185.65	$185.65	$185.60
Purchase #7	$40.50	7.627%	$43.5889	$43.59	$43.60	$43.60
7 purchase totals =	$972.53		$1,056.8220	$1,056.82	$1,056.85	$1,056.70