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	$46.95	9.611%	$51.4624	$51.46	$51.45	$51.50
Purchase #2	$91.65	12.592%	$103.1906	$103.19	$103.20	$103.20
Purchase #3	$234.65	6.262%	$249.3438	$249.34	$249.35	$249.30
Purchase #4	$50.87	13.716%	$57.8473	$57.85	$57.85	$57.80
Purchase #5	$36.27	8.509%	$39.3562	$39.36	$39.35	$39.40
Purchase #6	$115.86	10.425%	$127.9384	$127.94	$127.95	$127.90
Purchase #7	$89.61	7.857%	$96.6507	$96.65	$96.65	$96.70
7 purchase totals =	$665.86		$725.7894	$725.79	$725.80	$725.80