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	$17.90	9.610%	$19.6202	$19.62	$19.60	$19.60
Purchase #2	$65.59	11.365%	$73.0443	$73.04	$73.05	$73.00
Purchase #3	$227.86	6.764%	$243.2725	$243.27	$243.25	$243.30
Purchase #4	$13.89	5.320%	$14.6289	$14.63	$14.65	$14.60
Purchase #5	$100.30	4.764%	$105.0783	$105.08	$105.10	$105.10
Purchase #6	$156.85	13.565%	$178.1267	$178.13	$178.15	$178.10
Purchase #7	$143.45	13.524%	$162.8502	$162.85	$162.85	$162.90
7 purchase totals =	$725.84		$796.6211	$796.62	$796.65	$796.60