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	$115.94	6.459%	$123.4286	$123.43	$123.45	$123.40
Purchase #2	$190.39	10.630%	$210.6285	$210.63	$210.65	$210.60
Purchase #3	$227.31	8.531%	$246.7018	$246.70	$246.70	$246.70
Purchase #4	$153.78	12.216%	$172.5658	$172.57	$172.55	$172.60
Purchase #5	$60.85	9.665%	$66.7312	$66.73	$66.75	$66.70
Purchase #6	$193.43	11.217%	$215.127	$215.13	$215.15	$215.10
Purchase #7	$60.46	6.446%	$64.3573	$64.36	$64.35	$64.40
7 purchase totals =	$1,002.16		$1,099.5402	$1,099.55	$1,099.60	$1,099.50