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	$136.91	12.698%	$154.2948	$154.29	$154.30	$154.30
Purchase #2	$38.40	5.587%	$40.5454	$40.55	$40.55	$40.50
Purchase #3	$63.55	3.554%	$65.8086	$65.81	$65.80	$65.80
Purchase #4	$187.30	4.697%	$196.0975	$196.10	$196.10	$196.10
Purchase #5	$25.42	4.579%	$26.584	$26.58	$26.60	$26.60
Purchase #6	$150.33	11.493%	$167.6074	$167.61	$167.60	$167.60
Purchase #7	$21.50	12.362%	$24.1578	$24.16	$24.15	$24.20
7 purchase totals =	$623.41		$675.0955	$675.10	$675.10	$675.10