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	$12.64	5.678%	$13.3577	$13.36	$13.35	$13.40
Purchase #2	$241.26	6.126%	$256.0396	$256.04	$256.05	$256.00
Purchase #3	$180.49	8.852%	$196.467	$196.47	$196.45	$196.50
Purchase #4	$128.77	8.747%	$140.0335	$140.03	$140.05	$140.00
Purchase #5	$156.95	5.682%	$165.8679	$165.87	$165.85	$165.90
Purchase #6	$164.35	10.531%	$181.6577	$181.66	$181.65	$181.70
Purchase #7	$195.98	11.194%	$217.918	$217.92	$217.90	$217.90
7 purchase totals =	$1,080.44		$1,171.3414	$1,171.35	$1,171.30	$1,171.40