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	$45.65	13.702%	$51.905	$51.91	$51.90	$51.90
Purchase #2	$14.42	9.648%	$15.8112	$15.81	$15.80	$15.80
Purchase #3	$102.37	6.598%	$109.1244	$109.12	$109.10	$109.10
Purchase #4	$51.99	4.756%	$54.4626	$54.46	$54.45	$54.50
Purchase #5	$208.35	11.787%	$232.9082	$232.91	$232.90	$232.90
Purchase #6	$59.42	13.671%	$67.5433	$67.54	$67.55	$67.50
Purchase #7	$103.29	13.372%	$117.1019	$117.10	$117.10	$117.10
7 purchase totals =	$585.49		$648.8566	$648.85	$648.80	$648.80