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	$241.87	9.409%	$264.6275	$264.63	$264.65	$264.60
Purchase #2	$55.73	6.693%	$59.46	$59.46	$59.45	$59.50
Purchase #3	$113.82	6.487%	$121.2035	$121.20	$121.20	$121.20
Purchase #4	$196.85	4.597%	$205.8992	$205.90	$205.90	$205.90
Purchase #5	$71.72	10.635%	$79.3474	$79.35	$79.35	$79.30
Purchase #6	$78.90	4.752%	$82.6493	$82.65	$82.65	$82.60
Purchase #7	$153.91	8.538%	$167.0508	$167.05	$167.05	$167.10
7 purchase totals =	$912.80		$980.2377	$980.24	$980.25	$980.20