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	$244.53	10.439%	$270.0565	$270.06	$270.05	$270.10
Purchase #2	$92.83	8.685%	$100.8923	$100.89	$100.90	$100.90
Purchase #3	$171.89	11.854%	$192.2658	$192.27	$192.25	$192.30
Purchase #4	$85.36	5.292%	$89.8773	$89.88	$89.90	$89.90
Purchase #5	$16.29	3.409%	$16.8453	$16.85	$16.85	$16.80
Purchase #6	$166.63	3.647%	$172.707	$172.71	$172.70	$172.70
Purchase #7	$19.38	9.328%	$21.1878	$21.19	$21.20	$21.20
7 purchase totals =	$796.91		$863.8320	$863.85	$863.85	$863.90