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	$111.55	9.645%	$122.309	$122.31	$122.30	$122.30
Purchase #2	$49.78	9.238%	$54.3787	$54.38	$54.40	$54.40
Purchase #3	$83.34	13.138%	$94.2892	$94.29	$94.30	$94.30
Purchase #4	$41.80	5.500%	$44.099	$44.10	$44.10	$44.10
Purchase #5	$105.46	5.627%	$111.3942	$111.39	$111.40	$111.40
Purchase #6	$96.71	6.869%	$103.353	$103.35	$103.35	$103.40
Purchase #7	$34.53	13.120%	$39.0603	$39.06	$39.05	$39.10
7 purchase totals =	$523.17		$568.8834	$568.88	$568.90	$569.00