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	$10.68	8.535%	$11.5915	$11.59	$11.60	$11.60
Purchase #2	$171.54	10.240%	$189.1057	$189.11	$189.10	$189.10
Purchase #3	$232.29	13.663%	$264.0278	$264.03	$264.05	$264.00
Purchase #4	$128.63	11.526%	$143.4559	$143.46	$143.45	$143.50
Purchase #5	$137.58	10.632%	$152.2075	$152.21	$152.20	$152.20
Purchase #6	$121.86	12.584%	$137.1949	$137.19	$137.20	$137.20
Purchase #7	$105.47	5.480%	$111.2498	$111.25	$111.25	$111.20
7 purchase totals =	$908.05		$1,008.8331	$1,008.84	$1,008.85	$1,008.80