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	$237.87	9.660%	$260.8482	$260.85	$260.85	$260.80
Purchase #2	$196.34	13.651%	$223.1424	$223.14	$223.15	$223.10
Purchase #3	$176.99	10.797%	$196.0996	$196.10	$196.10	$196.10
Purchase #4	$111.42	6.398%	$118.5487	$118.55	$118.55	$118.50
Purchase #5	$154.55	7.180%	$165.6467	$165.65	$165.65	$165.60
Purchase #6	$144.92	10.551%	$160.2105	$160.21	$160.20	$160.20
Purchase #7	$201.60	4.198%	$210.0632	$210.06	$210.05	$210.10
7 purchase totals =	$1,223.69		$1,334.5593	$1,334.56	$1,334.55	$1,334.40