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	$178.98	5.493%	$188.8114	$188.81	$188.80	$188.80
Purchase #2	$119.82	6.148%	$127.1865	$127.19	$127.20	$127.20
Purchase #3	$59.43	12.504%	$66.8611	$66.86	$66.85	$66.90
Purchase #4	$105.48	12.384%	$118.5426	$118.54	$118.55	$118.50
Purchase #5	$81.55	5.265%	$85.8436	$85.84	$85.85	$85.80
Purchase #6	$50.53	8.473%	$54.8114	$54.81	$54.80	$54.80
Purchase #7	$22.99	6.122%	$24.3974	$24.40	$24.40	$24.40
7 purchase totals =	$618.78		$666.4540	$666.45	$666.45	$666.40