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	$47.51	3.646%	$49.2422	$49.24	$49.25	$49.20
Purchase #2	$92.87	9.372%	$101.5738	$101.57	$101.55	$101.60
Purchase #3	$101.82	9.589%	$111.5835	$111.58	$111.60	$111.60
Purchase #4	$208.86	5.325%	$219.9818	$219.98	$220.00	$220.00
Purchase #5	$106.59	11.527%	$118.8766	$118.88	$118.90	$118.90
Purchase #6	$228.37	7.448%	$245.379	$245.38	$245.40	$245.40
Purchase #7	$134.27	3.805%	$139.379	$139.38	$139.40	$139.40
7 purchase totals =	$920.29		$986.0159	$986.01	$986.10	$986.10