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	$100.56	6.735%	$107.3327	$107.33	$107.35	$107.30
Purchase #2	$103.87	13.393%	$117.7813	$117.78	$117.80	$117.80
Purchase #3	$242.49	6.747%	$258.8508	$258.85	$258.85	$258.90
Purchase #4	$39.87	7.534%	$42.8738	$42.87	$42.85	$42.90
Purchase #5	$177.69	4.311%	$185.3502	$185.35	$185.35	$185.40
Purchase #6	$127.79	11.643%	$142.6686	$142.67	$142.65	$142.70
Purchase #7	$113.47	12.232%	$127.3497	$127.35	$127.35	$127.30
7 purchase totals =	$905.74		$982.2071	$982.20	$982.20	$982.30