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	$136.67	12.778%	$154.1337	$154.13	$154.15	$154.10
Purchase #2	$117.82	10.858%	$130.6129	$130.61	$130.60	$130.60
Purchase #3	$106.59	9.392%	$116.6009	$116.60	$116.60	$116.60
Purchase #4	$116.35	9.179%	$127.0298	$127.03	$127.05	$127.00
Purchase #5	$250.25	4.515%	$261.5488	$261.55	$261.55	$261.50
Purchase #6	$67.39	6.645%	$71.8681	$71.87	$71.85	$71.90
Purchase #7	$115.92	10.622%	$128.233	$128.23	$128.25	$128.20
7 purchase totals =	$910.99		$990.0272	$990.02	$990.05	$989.90