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	$234.89	3.184%	$242.3689	$242.37	$242.35	$242.40
Purchase #2	$169.98	5.196%	$178.8122	$178.81	$178.80	$178.80
Purchase #3	$109.45	7.172%	$117.2998	$117.30	$117.30	$117.30
Purchase #4	$100.30	12.541%	$112.8786	$112.88	$112.90	$112.90
Purchase #5	$213.89	9.548%	$234.3122	$234.31	$234.30	$234.30
Purchase #6	$10.84	3.460%	$11.2151	$11.22	$11.20	$11.20
Purchase #7	$244.37	13.181%	$276.5804	$276.58	$276.60	$276.60
7 purchase totals =	$1,083.72		$1,173.4672	$1,173.47	$1,173.45	$1,173.50