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	$13.84	10.681%	$15.3183	$15.32	$15.30	$15.30
Purchase #2	$72.44	6.479%	$77.1334	$77.13	$77.15	$77.10
Purchase #3	$207.49	11.741%	$231.8514	$231.85	$231.85	$231.90
Purchase #4	$202.93	10.154%	$223.5355	$223.54	$223.55	$223.50
Purchase #5	$111.35	10.108%	$122.6053	$122.61	$122.60	$122.60
Purchase #6	$141.51	12.787%	$159.6049	$159.60	$159.60	$159.60
Purchase #7	$135.82	9.328%	$148.4893	$148.49	$148.50	$148.50
7 purchase totals =	$885.38		$978.5381	$978.54	$978.55	$978.50