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	$161.69	5.850%	$171.1489	$171.15	$171.15	$171.10
Purchase #2	$249.43	10.249%	$274.9941	$274.99	$275.00	$275.00
Purchase #3	$106.61	4.321%	$111.2166	$111.22	$111.20	$111.20
Purchase #4	$135.36	13.315%	$153.3832	$153.38	$153.40	$153.40
Purchase #5	$42.37	3.704%	$43.9394	$43.94	$43.95	$43.90
Purchase #6	$39.83	9.474%	$43.6035	$43.60	$43.60	$43.60
Purchase #7	$214.52	12.349%	$241.0111	$241.01	$241.00	$241.00
7 purchase totals =	$949.81		$1,039.2968	$1,039.29	$1,039.30	$1,039.20