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	$21.85	11.416%	$24.3444	$24.34	$24.35	$24.30
Purchase #2	$69.80	9.606%	$76.505	$76.51	$76.50	$76.50
Purchase #3	$72.96	8.166%	$78.9179	$78.92	$78.90	$78.90
Purchase #4	$226.69	6.561%	$241.5631	$241.56	$241.55	$241.60
Purchase #5	$30.59	13.745%	$34.7946	$34.79	$34.80	$34.80
Purchase #6	$91.97	5.532%	$97.0578	$97.06	$97.05	$97.10
Purchase #7	$118.63	4.435%	$123.8912	$123.89	$123.90	$123.90
7 purchase totals =	$632.49		$677.0740	$677.07	$677.05	$677.10