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	$243.56	6.562%	$259.5424	$259.54	$259.55	$259.50
Purchase #2	$146.96	13.176%	$166.3234	$166.32	$166.30	$166.30
Purchase #3	$35.82	12.397%	$40.2606	$40.26	$40.25	$40.30
Purchase #4	$27.91	3.229%	$28.8112	$28.81	$28.80	$28.80
Purchase #5	$140.31	7.593%	$150.9637	$150.96	$150.95	$151.00
Purchase #6	$102.85	13.442%	$116.6751	$116.68	$116.70	$116.70
Purchase #7	$175.63	6.648%	$187.3059	$187.31	$187.30	$187.30
7 purchase totals =	$873.04		$949.8823	$949.88	$949.85	$949.90