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	$113.68	8.464%	$123.3019	$123.30	$123.30	$123.30
Purchase #2	$123.42	12.593%	$138.9623	$138.96	$138.95	$139.00
Purchase #3	$91.26	9.264%	$99.7143	$99.71	$99.70	$99.70
Purchase #4	$137.78	13.768%	$156.7496	$156.75	$156.75	$156.70
Purchase #5	$29.98	7.339%	$32.1802	$32.18	$32.20	$32.20
Purchase #6	$99.87	12.158%	$112.0122	$112.01	$112.00	$112.00
Purchase #7	$141.34	8.759%	$153.72	$153.72	$153.70	$153.70
7 purchase totals =	$737.33		$816.6405	$816.63	$816.60	$816.60