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	$132.30	5.469%	$139.5355	$139.54	$139.55	$139.50
Purchase #2	$175.98	3.360%	$181.8929	$181.89	$181.90	$181.90
Purchase #3	$223.61	5.484%	$235.8728	$235.87	$235.85	$235.90
Purchase #4	$242.68	5.347%	$255.6561	$255.66	$255.65	$255.70
Purchase #5	$44.86	3.446%	$46.4059	$46.41	$46.40	$46.40
Purchase #6	$114.26	9.708%	$125.3524	$125.35	$125.35	$125.40
Purchase #7	$71.27	13.850%	$81.1409	$81.14	$81.15	$81.10
7 purchase totals =	$1,004.96		$1,065.8565	$1,065.86	$1,065.85	$1,065.90