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	$143.48	10.396%	$158.3962	$158.40	$158.40	$158.40
Purchase #2	$38.39	13.224%	$43.4667	$43.47	$43.45	$43.50
Purchase #3	$130.89	9.341%	$143.1164	$143.12	$143.10	$143.10
Purchase #4	$222.39	4.346%	$232.0551	$232.06	$232.05	$232.10
Purchase #5	$29.76	7.794%	$32.0795	$32.08	$32.10	$32.10
Purchase #6	$146.74	6.188%	$155.8203	$155.82	$155.80	$155.80
Purchase #7	$242.48	13.211%	$274.514	$274.51	$274.50	$274.50
7 purchase totals =	$954.13		$1,039.4482	$1,039.46	$1,039.40	$1,039.50