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	$99.42	11.856%	$111.2072	$111.21	$111.20	$111.20
Purchase #2	$47.77	9.257%	$52.1921	$52.19	$52.20	$52.20
Purchase #3	$66.92	9.829%	$73.4976	$73.50	$73.50	$73.50
Purchase #4	$219.53	12.652%	$247.3049	$247.30	$247.30	$247.30
Purchase #5	$127.46	10.372%	$140.6802	$140.68	$140.70	$140.70
Purchase #6	$111.51	10.787%	$123.5386	$123.54	$123.55	$123.50
Purchase #7	$45.95	10.337%	$50.6999	$50.70	$50.70	$50.70
7 purchase totals =	$718.56		$799.1205	$799.12	$799.15	$799.10