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	$145.94	6.208%	$155	$155.00	$155.00	$155.00
Purchase #2	$235.45	4.464%	$245.9605	$245.96	$245.95	$246.00
Purchase #3	$31.82	4.726%	$33.3238	$33.32	$33.30	$33.30
Purchase #4	$30.40	7.748%	$32.7554	$32.76	$32.75	$32.80
Purchase #5	$29.52	7.370%	$31.6956	$31.70	$31.70	$31.70
Purchase #6	$80.82	12.286%	$90.7495	$90.75	$90.75	$90.70
Purchase #7	$25.52	7.675%	$27.4787	$27.48	$27.50	$27.50
7 purchase totals =	$579.47		$616.9635	$616.97	$616.95	$617.00