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	$11.54	12.805%	$13.0177	$13.02	$13.00	$13.00
Purchase #2	$77.50	7.441%	$83.2668	$83.27	$83.25	$83.30
Purchase #3	$224.68	3.196%	$231.8608	$231.86	$231.85	$231.90
Purchase #4	$206.55	13.227%	$233.8704	$233.87	$233.85	$233.90
Purchase #5	$51.47	7.712%	$55.4394	$55.44	$55.45	$55.40
Purchase #6	$38.89	11.282%	$43.2776	$43.28	$43.30	$43.30
Purchase #7	$76.81	8.151%	$83.0708	$83.07	$83.05	$83.10
7 purchase totals =	$687.44		$743.8035	$743.81	$743.75	$743.90