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	$17.62	3.119%	$18.1696	$18.17	$18.15	$18.20
Purchase #2	$190.31	12.498%	$214.0949	$214.09	$214.10	$214.10
Purchase #3	$75.35	10.799%	$83.487	$83.49	$83.50	$83.50
Purchase #4	$201.25	5.386%	$212.0893	$212.09	$212.10	$212.10
Purchase #5	$96.82	3.761%	$100.4614	$100.46	$100.45	$100.50
Purchase #6	$18.63	7.550%	$20.0366	$20.04	$20.05	$20.00
Purchase #7	$119.70	6.284%	$127.2219	$127.22	$127.20	$127.20
7 purchase totals =	$719.68		$775.5607	$775.56	$775.55	$775.60