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	$20.37	5.386%	$21.4671	$21.47	$21.45	$21.50
Purchase #2	$37.85	6.395%	$40.2705	$40.27	$40.25	$40.30
Purchase #3	$89.37	6.102%	$94.8234	$94.82	$94.80	$94.80
Purchase #4	$145.58	7.257%	$156.1447	$156.14	$156.15	$156.10
Purchase #5	$137.71	7.680%	$148.2861	$148.29	$148.30	$148.30
Purchase #6	$87.43	10.575%	$96.6757	$96.68	$96.70	$96.70
Purchase #7	$201.51	10.425%	$222.5174	$222.52	$222.50	$222.50
7 purchase totals =	$719.82		$780.1849	$780.19	$780.15	$780.20