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	$115.39	4.497%	$120.5791	$120.58	$120.60	$120.60
Purchase #2	$98.30	4.653%	$102.8739	$102.87	$102.85	$102.90
Purchase #3	$117.49	5.453%	$123.8967	$123.90	$123.90	$123.90
Purchase #4	$76.31	9.844%	$83.822	$83.82	$83.80	$83.80
Purchase #5	$115.90	3.424%	$119.8684	$119.87	$119.85	$119.90
Purchase #6	$137.80	11.423%	$153.5409	$153.54	$153.55	$153.50
Purchase #7	$67.77	10.573%	$74.9353	$74.94	$74.95	$74.90
7 purchase totals =	$728.96		$779.5163	$779.52	$779.50	$779.50