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	$166.68	9.416%	$182.3746	$182.37	$182.35	$182.40
Purchase #2	$52.51	13.529%	$59.6141	$59.61	$59.60	$59.60
Purchase #3	$23.27	7.494%	$25.0139	$25.01	$25.00	$25.00
Purchase #4	$199.90	10.741%	$221.3713	$221.37	$221.35	$221.40
Purchase #5	$63.83	5.377%	$67.2621	$67.26	$67.25	$67.30
Purchase #6	$54.27	5.288%	$57.1398	$57.14	$57.15	$57.10
Purchase #7	$67.69	6.693%	$72.2205	$72.22	$72.20	$72.20
7 purchase totals =	$628.15		$684.9963	$684.98	$684.90	$685.00