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	$111.92	6.846%	$119.582	$119.58	$119.60	$119.60
Purchase #2	$132.65	13.376%	$150.3933	$150.39	$150.40	$150.40
Purchase #3	$145.97	10.474%	$161.2589	$161.26	$161.25	$161.30
Purchase #4	$52.39	13.471%	$59.4475	$59.45	$59.45	$59.40
Purchase #5	$241.83	5.706%	$255.6288	$255.63	$255.65	$255.60
Purchase #6	$29.67	10.307%	$32.7281	$32.73	$32.75	$32.70
Purchase #7	$168.45	8.434%	$182.6571	$182.66	$182.65	$182.70
7 purchase totals =	$882.88		$961.6957	$961.70	$961.75	$961.70