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	$17.98	11.429%	$20.0349	$20.03	$20.05	$20.00
Purchase #2	$233.71	9.297%	$255.438	$255.44	$255.45	$255.40
Purchase #3	$52.67	8.248%	$57.0142	$57.01	$57.00	$57.00
Purchase #4	$96.29	7.192%	$103.2152	$103.22	$103.20	$103.20
Purchase #5	$109.79	4.685%	$114.9337	$114.93	$114.95	$114.90
Purchase #6	$198.32	4.161%	$206.5721	$206.57	$206.55	$206.60
Purchase #7	$140.78	6.768%	$150.308	$150.31	$150.30	$150.30
7 purchase totals =	$849.54		$907.5161	$907.51	$907.50	$907.40