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	$46.68	9.518%	$51.123	$51.12	$51.10	$51.10
Purchase #2	$77.32	7.203%	$82.8894	$82.89	$82.90	$82.90
Purchase #3	$219.53	12.324%	$246.5849	$246.58	$246.60	$246.60
Purchase #4	$36.38	13.295%	$41.2167	$41.22	$41.20	$41.20
Purchase #5	$41.60	9.504%	$45.5537	$45.55	$45.55	$45.60
Purchase #6	$6.99	11.367%	$7.7846	$7.78	$7.80	$7.80
Purchase #7	$31.67	4.567%	$33.1164	$33.12	$33.10	$33.10
7 purchase totals =	$460.17		$508.2687	$508.26	$508.25	$508.30