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	$218.66	5.518%	$230.7257	$230.73	$230.75	$230.70
Purchase #2	$105.88	12.230%	$118.8291	$118.83	$118.85	$118.80
Purchase #3	$86.27	5.264%	$90.8113	$90.81	$90.80	$90.80
Purchase #4	$110.76	6.176%	$117.6005	$117.60	$117.60	$117.60
Purchase #5	$178.58	7.212%	$191.4592	$191.46	$191.45	$191.50
Purchase #6	$138.52	13.730%	$157.5388	$157.54	$157.55	$157.50
Purchase #7	$82.75	12.762%	$93.3106	$93.31	$93.30	$93.30
7 purchase totals =	$921.42		$1,000.2752	$1,000.28	$1,000.30	$1,000.20