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	$229.79	11.809%	$256.9259	$256.93	$256.95	$256.90
Purchase #2	$74.84	11.629%	$83.5431	$83.54	$83.55	$83.50
Purchase #3	$150.40	6.577%	$160.2918	$160.29	$160.30	$160.30
Purchase #4	$185.94	5.835%	$196.7896	$196.79	$196.80	$196.80
Purchase #5	$150.33	5.443%	$158.5125	$158.51	$158.50	$158.50
Purchase #6	$113.41	4.115%	$118.0768	$118.08	$118.10	$118.10
Purchase #7	$95.68	8.616%	$103.9238	$103.92	$103.90	$103.90
7 purchase totals =	$1,000.39		$1,078.0635	$1,078.06	$1,078.10	$1,078.00