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	$112.72	4.852%	$118.1892	$118.19	$118.20	$118.20
Purchase #2	$52.58	12.605%	$59.2077	$59.21	$59.20	$59.20
Purchase #3	$73.31	12.322%	$82.3433	$82.34	$82.35	$82.30
Purchase #4	$63.97	7.207%	$68.5803	$68.58	$68.60	$68.60
Purchase #5	$123.29	12.817%	$139.0921	$139.09	$139.10	$139.10
Purchase #6	$143.86	7.806%	$155.0897	$155.09	$155.10	$155.10
Purchase #7	$157.84	13.552%	$179.2305	$179.23	$179.25	$179.20
7 purchase totals =	$727.57		$801.7328	$801.73	$801.80	$801.70