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	$111.60	10.615%	$123.4463	$123.45	$123.45	$123.40
Purchase #2	$59.34	10.783%	$65.7386	$65.74	$65.75	$65.70
Purchase #3	$30.31	8.359%	$32.8436	$32.84	$32.85	$32.80
Purchase #4	$238.77	7.440%	$256.5345	$256.53	$256.55	$256.50
Purchase #5	$168.80	9.186%	$184.306	$184.31	$184.30	$184.30
Purchase #6	$31.32	8.807%	$34.0784	$34.08	$34.10	$34.10
Purchase #7	$147.86	10.203%	$162.9462	$162.95	$162.95	$162.90
7 purchase totals =	$788.00		$859.8936	$859.90	$859.95	$859.70