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	$247.83	3.134%	$255.597	$255.60	$255.60	$255.60
Purchase #2	$109.35	12.546%	$123.0691	$123.07	$123.05	$123.10
Purchase #3	$85.33	9.453%	$93.3962	$93.40	$93.40	$93.40
Purchase #4	$193.28	3.357%	$199.7684	$199.77	$199.75	$199.80
Purchase #5	$162.48	12.160%	$182.2376	$182.24	$182.25	$182.20
Purchase #6	$34.36	10.309%	$37.9022	$37.90	$37.90	$37.90
Purchase #7	$62.54	13.211%	$70.8022	$70.80	$70.80	$70.80
7 purchase totals =	$895.17		$962.7727	$962.78	$962.75	$962.80