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	$237.95	13.679%	$270.4992	$270.50	$270.50	$270.50
Purchase #2	$225.34	8.752%	$245.0618	$245.06	$245.05	$245.10
Purchase #3	$163.56	5.314%	$172.2516	$172.25	$172.25	$172.30
Purchase #4	$111.39	10.542%	$123.1327	$123.13	$123.15	$123.10
Purchase #5	$113.90	5.491%	$120.1542	$120.15	$120.15	$120.20
Purchase #6	$227.28	8.257%	$246.0465	$246.05	$246.05	$246.00
Purchase #7	$152.41	10.139%	$167.8628	$167.86	$167.85	$167.90
7 purchase totals =	$1,231.83		$1,345.0088	$1,345.00	$1,345.00	$1,345.10