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	$66.34	9.431%	$72.5965	$72.60	$72.60	$72.60
Purchase #2	$27.81	7.300%	$29.8401	$29.84	$29.85	$29.80
Purchase #3	$187.29	7.464%	$201.2693	$201.27	$201.25	$201.30
Purchase #4	$156.38	3.747%	$162.2396	$162.24	$162.25	$162.20
Purchase #5	$75.71	12.270%	$84.9996	$85.00	$85.00	$85.00
Purchase #6	$29.52	10.183%	$32.526	$32.53	$32.55	$32.50
Purchase #7	$248.42	3.159%	$256.2676	$256.27	$256.25	$256.30
7 purchase totals =	$791.47		$839.7387	$839.75	$839.75	$839.70