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	$16.85	11.109%	$18.7219	$18.72	$18.70	$18.70
Purchase #2	$41.60	7.771%	$44.8327	$44.83	$44.85	$44.80
Purchase #3	$229.39	5.190%	$241.2953	$241.30	$241.30	$241.30
Purchase #4	$78.92	8.346%	$85.5067	$85.51	$85.50	$85.50
Purchase #5	$107.89	12.632%	$121.5187	$121.52	$121.50	$121.50
Purchase #6	$151.30	7.239%	$162.2526	$162.25	$162.25	$162.30
Purchase #7	$240.46	3.347%	$248.5082	$248.51	$248.50	$248.50
7 purchase totals =	$866.41		$922.6361	$922.64	$922.60	$922.60