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	$89.40	11.411%	$99.6014	$99.60	$99.60	$99.60
Purchase #2	$163.85	4.819%	$171.7459	$171.75	$171.75	$171.70
Purchase #3	$142.84	8.154%	$154.4872	$154.49	$154.50	$154.50
Purchase #4	$138.37	3.337%	$142.9874	$142.99	$143.00	$143.00
Purchase #5	$222.85	6.747%	$237.8857	$237.89	$237.90	$237.90
Purchase #6	$76.34	8.259%	$82.6449	$82.64	$82.65	$82.60
Purchase #7	$152.51	10.273%	$168.1774	$168.18	$168.20	$168.20
7 purchase totals =	$986.16		$1,057.5299	$1,057.54	$1,057.60	$1,057.50