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	$15.58	3.546%	$16.1325	$16.13	$16.15	$16.10
Purchase #2	$56.47	5.376%	$59.5058	$59.51	$59.50	$59.50
Purchase #3	$239.64	9.119%	$261.4928	$261.49	$261.50	$261.50
Purchase #4	$216.45	11.557%	$241.4651	$241.47	$241.45	$241.50
Purchase #5	$44.54	7.366%	$47.8208	$47.82	$47.80	$47.80
Purchase #6	$131.78	7.557%	$141.7386	$141.74	$141.75	$141.70
Purchase #7	$112.66	9.817%	$123.7198	$123.72	$123.70	$123.70
7 purchase totals =	$817.12		$891.8754	$891.88	$891.85	$891.80