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	$104.37	3.826%	$108.3632	$108.36	$108.35	$108.40
Purchase #2	$103.98	5.328%	$109.5201	$109.52	$109.50	$109.50
Purchase #3	$208.88	8.453%	$226.5366	$226.54	$226.55	$226.50
Purchase #4	$45.25	13.728%	$51.4619	$51.46	$51.45	$51.50
Purchase #5	$24.52	3.816%	$25.4557	$25.46	$25.45	$25.50
Purchase #6	$107.84	10.792%	$119.4781	$119.48	$119.50	$119.50
Purchase #7	$35.30	11.443%	$39.3394	$39.34	$39.35	$39.30
7 purchase totals =	$630.14		$680.1550	$680.16	$680.15	$680.20