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	$11.89	5.139%	$12.501	$12.50	$12.50	$12.50
Purchase #2	$95.99	5.769%	$101.5277	$101.53	$101.55	$101.50
Purchase #3	$74.96	3.334%	$77.4592	$77.46	$77.45	$77.50
Purchase #4	$59.57	10.826%	$66.019	$66.02	$66.00	$66.00
Purchase #5	$230.88	3.247%	$238.3767	$238.38	$238.40	$238.40
Purchase #6	$234.98	6.430%	$250.0892	$250.09	$250.10	$250.10
Purchase #7	$142.83	8.148%	$154.4678	$154.47	$154.45	$154.50
7 purchase totals =	$851.10		$900.4406	$900.45	$900.45	$900.50