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	$229.86	7.509%	$247.1202	$247.12	$247.10	$247.10
Purchase #2	$133.84	5.720%	$141.4956	$141.50	$141.50	$141.50
Purchase #3	$115.33	7.390%	$123.8529	$123.85	$123.85	$123.90
Purchase #4	$98.50	5.460%	$103.8781	$103.88	$103.90	$103.90
Purchase #5	$116.60	9.779%	$128.0023	$128.00	$128.00	$128.00
Purchase #6	$26.40	4.495%	$27.5867	$27.59	$27.60	$27.60
Purchase #7	$37.32	10.572%	$41.2655	$41.27	$41.25	$41.30
7 purchase totals =	$757.85		$813.2013	$813.21	$813.20	$813.30