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	$206.51	10.202%	$227.5782	$227.58	$227.60	$227.60
Purchase #2	$20.36	4.108%	$21.1964	$21.20	$21.20	$21.20
Purchase #3	$102.87	8.476%	$111.5893	$111.59	$111.60	$111.60
Purchase #4	$180.38	9.869%	$198.1817	$198.18	$198.20	$198.20
Purchase #5	$104.91	6.842%	$112.0879	$112.09	$112.10	$112.10
Purchase #6	$72.79	4.600%	$76.1383	$76.14	$76.15	$76.10
Purchase #7	$101.48	11.616%	$113.2679	$113.27	$113.25	$113.30
7 purchase totals =	$789.30		$860.0397	$860.05	$860.10	$860.10