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	$233.86	9.247%	$255.485	$255.49	$255.50	$255.50
Purchase #2	$121.31	8.656%	$131.8106	$131.81	$131.80	$131.80
Purchase #3	$42.77	8.278%	$46.3105	$46.31	$46.30	$46.30
Purchase #4	$215.32	9.752%	$236.318	$236.32	$236.30	$236.30
Purchase #5	$127.38	9.115%	$138.9907	$138.99	$139.00	$139.00
Purchase #6	$60.97	10.449%	$67.3408	$67.34	$67.35	$67.30
Purchase #7	$129.81	9.465%	$142.0965	$142.10	$142.10	$142.10
7 purchase totals =	$931.42		$1,018.3521	$1,018.36	$1,018.35	$1,018.30