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	$32.49	6.528%	$34.6109	$34.61	$34.60	$34.60
Purchase #2	$136.47	13.635%	$155.0777	$155.08	$155.10	$155.10
Purchase #3	$39.46	10.460%	$43.5875	$43.59	$43.60	$43.60
Purchase #4	$246.97	13.713%	$280.837	$280.84	$280.85	$280.80
Purchase #5	$141.58	12.619%	$159.446	$159.45	$159.45	$159.40
Purchase #6	$19.92	7.582%	$21.4303	$21.43	$21.45	$21.40
Purchase #7	$232.27	4.744%	$243.2889	$243.29	$243.30	$243.30
7 purchase totals =	$849.16		$938.2783	$938.29	$938.35	$938.20