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	$233.62	9.787%	$256.4844	$256.48	$256.50	$256.50
Purchase #2	$137.45	4.815%	$144.0682	$144.07	$144.05	$144.10
Purchase #3	$147.41	13.247%	$166.9374	$166.94	$166.95	$166.90
Purchase #4	$39.82	6.459%	$42.392	$42.39	$42.40	$42.40
Purchase #5	$192.43	8.253%	$208.3112	$208.31	$208.30	$208.30
Purchase #6	$212.88	12.804%	$240.1372	$240.14	$240.15	$240.10
Purchase #7	$19.50	7.762%	$21.0136	$21.01	$21.00	$21.00
7 purchase totals =	$983.11		$1,079.3440	$1,079.34	$1,079.35	$1,079.30