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	$104.81	4.196%	$109.2078	$109.21	$109.20	$109.20
Purchase #2	$159.97	4.276%	$166.8103	$166.81	$166.80	$166.80
Purchase #3	$231.57	13.259%	$262.2739	$262.27	$262.25	$262.30
Purchase #4	$82.68	7.865%	$89.1828	$89.18	$89.20	$89.20
Purchase #5	$82.67	9.822%	$90.7898	$90.79	$90.80	$90.80
Purchase #6	$155.66	11.366%	$173.3523	$173.35	$173.35	$173.40
Purchase #7	$114.34	10.605%	$126.4658	$126.47	$126.45	$126.50
7 purchase totals =	$931.70		$1,018.0827	$1,018.08	$1,018.05	$1,018.20