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	$77.35	10.404%	$85.3975	$85.40	$85.40	$85.40
Purchase #2	$86.64	8.393%	$93.9117	$93.91	$93.90	$93.90
Purchase #3	$247.67	13.715%	$281.6379	$281.64	$281.65	$281.60
Purchase #4	$78.38	4.602%	$81.987	$81.99	$82.00	$82.00
Purchase #5	$200.35	4.681%	$209.7284	$209.73	$209.75	$209.70
Purchase #6	$76.71	7.718%	$82.6305	$82.63	$82.65	$82.60
Purchase #7	$118.79	4.304%	$123.9027	$123.90	$123.90	$123.90
7 purchase totals =	$885.89		$959.1957	$959.20	$959.25	$959.10