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	$230.43	10.395%	$254.3832	$254.38	$254.40	$254.40
Purchase #2	$173.43	9.827%	$190.473	$190.47	$190.45	$190.50
Purchase #3	$174.97	6.554%	$186.4375	$186.44	$186.45	$186.40
Purchase #4	$189.92	9.839%	$208.6062	$208.61	$208.60	$208.60
Purchase #5	$95.45	4.620%	$99.8598	$99.86	$99.85	$99.90
Purchase #6	$70.81	9.556%	$77.5766	$77.58	$77.60	$77.60
Purchase #7	$114.72	8.676%	$124.6731	$124.67	$124.65	$124.70
7 purchase totals =	$1,049.73		$1,142.0094	$1,142.01	$1,142.00	$1,142.10