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	$61.28	8.851%	$66.7039	$66.70	$66.70	$66.70
Purchase #2	$30.72	6.299%	$32.6551	$32.66	$32.65	$32.70
Purchase #3	$172.46	7.331%	$185.103	$185.10	$185.10	$185.10
Purchase #4	$40.60	8.230%	$43.9414	$43.94	$43.95	$43.90
Purchase #5	$137.34	13.710%	$156.1693	$156.17	$156.15	$156.20
Purchase #6	$128.85	3.134%	$132.8882	$132.89	$132.90	$132.90
Purchase #7	$149.71	8.764%	$162.8306	$162.83	$162.85	$162.80
7 purchase totals =	$720.96		$780.2915	$780.29	$780.30	$780.30