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	$27.83	13.595%	$31.6135	$31.61	$31.60	$31.60
Purchase #2	$223.72	4.354%	$233.4608	$233.46	$233.45	$233.50
Purchase #3	$191.31	13.250%	$216.6586	$216.66	$216.65	$216.70
Purchase #4	$118.33	3.488%	$122.4574	$122.46	$122.45	$122.50
Purchase #5	$139.34	4.597%	$145.7455	$145.75	$145.75	$145.70
Purchase #6	$188.31	11.859%	$210.6417	$210.64	$210.65	$210.60
Purchase #7	$19.91	9.860%	$21.8731	$21.87	$21.85	$21.90
7 purchase totals =	$908.75		$982.4506	$982.45	$982.40	$982.50