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	$27.87	5.457%	$29.3909	$29.39	$29.40	$29.40
Purchase #2	$150.38	11.607%	$167.8346	$167.83	$167.85	$167.80
Purchase #3	$100.74	12.821%	$113.6559	$113.66	$113.65	$113.70
Purchase #4	$68.98	7.143%	$73.9072	$73.91	$73.90	$73.90
Purchase #5	$84.38	7.138%	$90.403	$90.40	$90.40	$90.40
Purchase #6	$54.91	5.341%	$57.8427	$57.84	$57.85	$57.80
Purchase #7	$80.48	3.531%	$83.3217	$83.32	$83.30	$83.30
7 purchase totals =	$567.74		$616.3560	$616.35	$616.35	$616.30