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	$118.63	10.443%	$131.0185	$131.02	$131.00	$131.00
Purchase #2	$133.61	9.612%	$146.4526	$146.45	$146.45	$146.50
Purchase #3	$164.50	9.702%	$180.4598	$180.46	$180.45	$180.50
Purchase #4	$58.85	6.702%	$62.7941	$62.79	$62.80	$62.80
Purchase #5	$215.58	7.449%	$231.6386	$231.64	$231.65	$231.60
Purchase #6	$54.75	3.407%	$56.6153	$56.62	$56.60	$56.60
Purchase #7	$89.87	12.466%	$101.0732	$101.07	$101.05	$101.10
7 purchase totals =	$835.79		$910.0521	$910.05	$910.00	$910.10