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	$96.76	6.243%	$102.8007	$102.80	$102.80	$102.80
Purchase #2	$86.81	3.484%	$89.8345	$89.83	$89.85	$89.80
Purchase #3	$153.33	12.516%	$172.5208	$172.52	$172.50	$172.50
Purchase #4	$115.54	10.418%	$127.577	$127.58	$127.60	$127.60
Purchase #5	$167.99	9.232%	$183.4988	$183.50	$183.50	$183.50
Purchase #6	$134.50	9.240%	$146.9278	$146.93	$146.95	$146.90
Purchase #7	$184.64	4.193%	$192.382	$192.38	$192.40	$192.40
7 purchase totals =	$939.57		$1,015.5416	$1,015.54	$1,015.60	$1,015.50