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	$205.35	5.564%	$216.7757	$216.78	$216.80	$216.80
Purchase #2	$219.39	11.436%	$244.4794	$244.48	$244.50	$244.50
Purchase #3	$220.31	7.282%	$236.353	$236.35	$236.35	$236.40
Purchase #4	$36.33	10.115%	$40.0048	$40.00	$40.00	$40.00
Purchase #5	$129.86	9.798%	$142.5837	$142.58	$142.60	$142.60
Purchase #6	$112.30	9.454%	$122.9168	$122.92	$122.90	$122.90
Purchase #7	$80.87	11.357%	$90.0544	$90.05	$90.05	$90.10
7 purchase totals =	$1,004.41		$1,093.1678	$1,093.16	$1,093.20	$1,093.30