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	$173.45	4.425%	$181.1252	$181.13	$181.15	$181.10
Purchase #2	$47.56	12.249%	$53.3856	$53.39	$53.40	$53.40
Purchase #3	$212.76	9.265%	$232.4722	$232.47	$232.45	$232.50
Purchase #4	$36.79	12.577%	$41.4171	$41.42	$41.40	$41.40
Purchase #5	$108.27	5.648%	$114.3851	$114.39	$114.40	$114.40
Purchase #6	$48.98	10.785%	$54.2625	$54.26	$54.25	$54.30
Purchase #7	$242.51	9.495%	$265.5363	$265.54	$265.55	$265.50
7 purchase totals =	$870.32		$942.5840	$942.60	$942.60	$942.60