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	$240.82	12.646%	$271.2741	$271.27	$271.25	$271.30
Purchase #2	$117.99	12.264%	$132.4603	$132.46	$132.45	$132.50
Purchase #3	$145.59	10.471%	$160.8347	$160.83	$160.85	$160.80
Purchase #4	$140.80	11.139%	$156.4837	$156.48	$156.50	$156.50
Purchase #5	$24.75	11.216%	$27.526	$27.53	$27.55	$27.50
Purchase #6	$113.77	8.263%	$123.1708	$123.17	$123.15	$123.20
Purchase #7	$83.34	8.526%	$90.4456	$90.45	$90.45	$90.40
7 purchase totals =	$867.06		$962.1952	$962.19	$962.20	$962.20