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	$76.79	7.433%	$82.4978	$82.50	$82.50	$82.50
Purchase #2	$102.89	13.311%	$116.5857	$116.59	$116.60	$116.60
Purchase #3	$24.55	12.681%	$27.6632	$27.66	$27.65	$27.70
Purchase #4	$175.37	4.390%	$183.0687	$183.07	$183.05	$183.10
Purchase #5	$183.33	8.218%	$198.3961	$198.40	$198.40	$198.40
Purchase #6	$246.30	5.769%	$260.509	$260.51	$260.50	$260.50
Purchase #7	$133.97	9.288%	$146.4131	$146.41	$146.40	$146.40
7 purchase totals =	$943.20		$1,015.1336	$1,015.14	$1,015.10	$1,015.20