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	$212.98	13.265%	$241.2318	$241.23	$241.25	$241.20
Purchase #2	$113.77	11.456%	$126.8035	$126.80	$126.80	$126.80
Purchase #3	$112.62	13.633%	$127.9735	$127.97	$127.95	$128.00
Purchase #4	$176.34	7.416%	$189.4174	$189.42	$189.40	$189.40
Purchase #5	$37.94	13.544%	$43.0786	$43.08	$43.10	$43.10
Purchase #6	$32.37	3.380%	$33.4641	$33.46	$33.45	$33.50
Purchase #7	$148.32	12.607%	$167.0187	$167.02	$167.00	$167.00
7 purchase totals =	$834.34		$928.9876	$928.98	$928.95	$929.00