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	$222.89	13.621%	$253.2498	$253.25	$253.25	$253.20
Purchase #2	$135.27	10.207%	$149.077	$149.08	$149.10	$149.10
Purchase #3	$17.87	12.436%	$20.0923	$20.09	$20.10	$20.10
Purchase #4	$229.42	13.556%	$260.5202	$260.52	$260.50	$260.50
Purchase #5	$132.78	10.264%	$146.4085	$146.41	$146.40	$146.40
Purchase #6	$123.85	7.345%	$132.9468	$132.95	$132.95	$132.90
Purchase #7	$112.79	4.700%	$118.0911	$118.09	$118.10	$118.10
7 purchase totals =	$974.87		$1,080.3857	$1,080.39	$1,080.40	$1,080.30