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	$51.54	5.828%	$54.5438	$54.54	$54.55	$54.50
Purchase #2	$145.89	6.356%	$155.1628	$155.16	$155.15	$155.20
Purchase #3	$199.39	7.830%	$215.0022	$215.00	$215.00	$215.00
Purchase #4	$9.41	13.616%	$10.6913	$10.69	$10.70	$10.70
Purchase #5	$178.66	9.756%	$196.0901	$196.09	$196.10	$196.10
Purchase #6	$92.95	12.157%	$104.2499	$104.25	$104.25	$104.20
Purchase #7	$164.59	10.161%	$181.314	$181.31	$181.30	$181.30
7 purchase totals =	$842.43		$917.0541	$917.04	$917.05	$917.00