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	$227.37	12.368%	$255.4911	$255.49	$255.50	$255.50
Purchase #2	$83.49	8.179%	$90.3186	$90.32	$90.30	$90.30
Purchase #3	$227.78	7.672%	$245.2553	$245.26	$245.25	$245.30
Purchase #4	$145.30	9.643%	$159.3113	$159.31	$159.30	$159.30
Purchase #5	$185.90	13.160%	$210.3644	$210.36	$210.35	$210.40
Purchase #6	$185.70	10.177%	$204.5987	$204.60	$204.60	$204.60
Purchase #7	$104.73	3.736%	$108.6427	$108.64	$108.65	$108.60
7 purchase totals =	$1,160.27		$1,273.9821	$1,273.98	$1,273.95	$1,274.00