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	$123.94	6.286%	$131.7309	$131.73	$131.75	$131.70
Purchase #2	$158.25	10.269%	$174.5007	$174.50	$174.50	$174.50
Purchase #3	$10.66	11.447%	$11.8803	$11.88	$11.90	$11.90
Purchase #4	$137.33	11.419%	$153.0117	$153.01	$153.00	$153.00
Purchase #5	$76.50	11.639%	$85.4038	$85.40	$85.40	$85.40
Purchase #6	$207.76	13.509%	$235.8263	$235.83	$235.85	$235.80
Purchase #7	$50.42	6.686%	$53.7911	$53.79	$53.80	$53.80
7 purchase totals =	$764.86		$846.1448	$846.14	$846.20	$846.10