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	$204.85	10.559%	$226.4801	$226.48	$226.50	$226.50
Purchase #2	$91.77	13.605%	$104.2553	$104.26	$104.25	$104.30
Purchase #3	$158.31	5.858%	$167.5838	$167.58	$167.60	$167.60
Purchase #4	$222.56	8.673%	$241.8626	$241.86	$241.85	$241.90
Purchase #5	$183.43	3.774%	$190.3526	$190.35	$190.35	$190.40
Purchase #6	$28.59	9.823%	$31.3984	$31.40	$31.40	$31.40
Purchase #7	$25.32	8.736%	$27.532	$27.53	$27.55	$27.50
7 purchase totals =	$914.83		$989.4648	$989.46	$989.50	$989.60