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	$83.90	8.288%	$90.8536	$90.85	$90.85	$90.90
Purchase #2	$70.43	9.843%	$77.3624	$77.36	$77.35	$77.40
Purchase #3	$97.50	5.833%	$103.1872	$103.19	$103.20	$103.20
Purchase #4	$29.66	5.404%	$31.2628	$31.26	$31.25	$31.30
Purchase #5	$90.93	10.627%	$100.5931	$100.59	$100.60	$100.60
Purchase #6	$219.72	5.521%	$231.8507	$231.85	$231.85	$231.90
Purchase #7	$38.95	5.836%	$41.2231	$41.22	$41.20	$41.20
7 purchase totals =	$631.09		$676.3329	$676.32	$676.30	$676.50