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	$33.93	11.747%	$37.9158	$37.92	$37.90	$37.90
Purchase #2	$90.56	10.291%	$99.8795	$99.88	$99.90	$99.90
Purchase #3	$238.69	7.613%	$256.8615	$256.86	$256.85	$256.90
Purchase #4	$102.99	13.555%	$116.9503	$116.95	$116.95	$117.00
Purchase #5	$194.86	10.555%	$215.4275	$215.43	$215.45	$215.40
Purchase #6	$86.99	3.844%	$90.3339	$90.33	$90.35	$90.30
Purchase #7	$114.96	6.208%	$122.0967	$122.10	$122.10	$122.10
7 purchase totals =	$862.98		$939.4652	$939.47	$939.50	$939.50