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	$50.84	9.742%	$55.7928	$55.79	$55.80	$55.80
Purchase #2	$216.69	7.766%	$233.5181	$233.52	$233.50	$233.50
Purchase #3	$34.83	12.484%	$39.1782	$39.18	$39.20	$39.20
Purchase #4	$215.47	6.806%	$230.1349	$230.13	$230.15	$230.10
Purchase #5	$75.38	6.233%	$80.0784	$80.08	$80.10	$80.10
Purchase #6	$110.32	12.834%	$124.4785	$124.48	$124.50	$124.50
Purchase #7	$172.43	7.533%	$185.4192	$185.42	$185.40	$185.40
7 purchase totals =	$875.96		$948.6001	$948.60	$948.65	$948.60