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	$68.36	12.401%	$76.8373	$76.84	$76.85	$76.80
Purchase #2	$74.99	4.723%	$78.5318	$78.53	$78.55	$78.50
Purchase #3	$55.74	8.458%	$60.4545	$60.45	$60.45	$60.50
Purchase #4	$40.68	11.553%	$45.3798	$45.38	$45.40	$45.40
Purchase #5	$177.78	7.105%	$190.4113	$190.41	$190.40	$190.40
Purchase #6	$32.46	11.522%	$36.2	$36.20	$36.20	$36.20
Purchase #7	$76.66	7.824%	$82.6579	$82.66	$82.65	$82.70
7 purchase totals =	$526.67		$570.4726	$570.47	$570.50	$570.50