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	$31.28	7.700%	$33.6886	$33.69	$33.70	$33.70
Purchase #2	$238.75	10.283%	$263.3007	$263.30	$263.30	$263.30
Purchase #3	$108.98	13.422%	$123.6073	$123.61	$123.60	$123.60
Purchase #4	$134.79	10.770%	$149.3069	$149.31	$149.30	$149.30
Purchase #5	$112.27	6.426%	$119.4845	$119.48	$119.50	$119.50
Purchase #6	$138.53	4.286%	$144.4674	$144.47	$144.45	$144.50
Purchase #7	$83.51	3.555%	$86.4788	$86.48	$86.50	$86.50
7 purchase totals =	$848.11		$920.3342	$920.34	$920.35	$920.40