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	$235.72	10.431%	$260.308	$260.31	$260.30	$260.30
Purchase #2	$159.65	12.313%	$179.3077	$179.31	$179.30	$179.30
Purchase #3	$171.51	5.501%	$180.9448	$180.94	$180.95	$180.90
Purchase #4	$52.75	4.140%	$54.9339	$54.93	$54.95	$54.90
Purchase #5	$40.57	4.776%	$42.5076	$42.51	$42.50	$42.50
Purchase #6	$30.88	10.826%	$34.2231	$34.22	$34.20	$34.20
Purchase #7	$148.58	5.124%	$156.1932	$156.19	$156.20	$156.20
7 purchase totals =	$839.66		$908.4183	$908.41	$908.40	$908.30