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	$220.90	8.534%	$239.7516	$239.75	$239.75	$239.80
Purchase #2	$209.34	13.754%	$238.1326	$238.13	$238.15	$238.10
Purchase #3	$69.60	4.396%	$72.6596	$72.66	$72.65	$72.70
Purchase #4	$106.33	11.333%	$118.3804	$118.38	$118.40	$118.40
Purchase #5	$78.60	9.670%	$86.2006	$86.20	$86.20	$86.20
Purchase #6	$64.69	12.137%	$72.5414	$72.54	$72.55	$72.50
Purchase #7	$159.30	6.439%	$169.5573	$169.56	$169.55	$169.60
7 purchase totals =	$908.76		$997.2235	$997.22	$997.25	$997.30