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	$128.92	9.377%	$141.0088	$141.01	$141.00	$141.00
Purchase #2	$167.51	11.406%	$186.6162	$186.62	$186.60	$186.60
Purchase #3	$134.57	13.285%	$152.4476	$152.45	$152.45	$152.40
Purchase #4	$10.38	4.371%	$10.8337	$10.83	$10.85	$10.80
Purchase #5	$7.27	8.870%	$7.9148	$7.91	$7.90	$7.90
Purchase #6	$214.33	5.311%	$225.7131	$225.71	$225.70	$225.70
Purchase #7	$174.65	6.770%	$186.4738	$186.47	$186.45	$186.50
7 purchase totals =	$837.63		$911.0080	$911.00	$910.95	$910.90