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	$151.45	13.461%	$171.8367	$171.84	$171.85	$171.80
Purchase #2	$173.31	13.130%	$196.0656	$196.07	$196.05	$196.10
Purchase #3	$146.90	11.312%	$163.5173	$163.52	$163.50	$163.50
Purchase #4	$45.52	7.597%	$48.9782	$48.98	$49.00	$49.00
Purchase #5	$213.57	7.527%	$229.6454	$229.65	$229.65	$229.60
Purchase #6	$104.69	6.724%	$111.7294	$111.73	$111.75	$111.70
Purchase #7	$156.98	9.343%	$171.6466	$171.65	$171.65	$171.60
7 purchase totals =	$992.42		$1,093.4192	$1,093.44	$1,093.45	$1,093.30