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	$234.36	11.599%	$261.5434	$261.54	$261.55	$261.50
Purchase #2	$87.43	13.402%	$99.1474	$99.15	$99.15	$99.10
Purchase #3	$205.63	3.501%	$212.8291	$212.83	$212.85	$212.80
Purchase #4	$192.25	6.849%	$205.4172	$205.42	$205.40	$205.40
Purchase #5	$162.43	6.499%	$172.9863	$172.99	$173.00	$173.00
Purchase #6	$137.85	7.696%	$148.4589	$148.46	$148.45	$148.50
Purchase #7	$141.68	9.757%	$155.5037	$155.50	$155.50	$155.50
7 purchase totals =	$1,161.63		$1,255.8860	$1,255.89	$1,255.90	$1,255.80