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	$123.38	13.295%	$139.7834	$139.78	$139.80	$139.80
Purchase #2	$192.59	6.561%	$205.2258	$205.23	$205.25	$205.20
Purchase #3	$172.95	12.378%	$194.3578	$194.36	$194.35	$194.40
Purchase #4	$109.41	6.341%	$116.3477	$116.35	$116.35	$116.30
Purchase #5	$172.61	7.169%	$184.9844	$184.98	$185.00	$185.00
Purchase #6	$131.50	11.571%	$146.7159	$146.72	$146.70	$146.70
Purchase #7	$84.41	11.864%	$94.4244	$94.42	$94.40	$94.40
7 purchase totals =	$986.85		$1,081.8394	$1,081.84	$1,081.85	$1,081.80