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	$80.35	4.382%	$83.8709	$83.87	$83.85	$83.90
Purchase #2	$60.36	3.314%	$62.3603	$62.36	$62.35	$62.40
Purchase #3	$80.88	10.826%	$89.6361	$89.64	$89.65	$89.60
Purchase #4	$212.25	8.791%	$230.9089	$230.91	$230.90	$230.90
Purchase #5	$112.36	9.618%	$123.1668	$123.17	$123.15	$123.20
Purchase #6	$230.50	3.173%	$237.8138	$237.81	$237.80	$237.80
Purchase #7	$58.94	4.523%	$61.6059	$61.61	$61.60	$61.60
7 purchase totals =	$835.64		$889.3627	$889.37	$889.30	$889.40