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	$9.31	12.298%	$10.4549	$10.45	$10.45	$10.50
Purchase #2	$133.31	8.639%	$144.8267	$144.83	$144.85	$144.80
Purchase #3	$89.81	3.383%	$92.8483	$92.85	$92.85	$92.80
Purchase #4	$221.89	4.855%	$232.6628	$232.66	$232.65	$232.70
Purchase #5	$20.38	7.440%	$21.8963	$21.90	$21.90	$21.90
Purchase #6	$33.44	10.268%	$36.8736	$36.87	$36.85	$36.90
Purchase #7	$24.77	11.783%	$27.6886	$27.69	$27.70	$27.70
7 purchase totals =	$532.91		$567.2512	$567.25	$567.25	$567.30