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	$56.26	12.575%	$63.3347	$63.33	$63.35	$63.30
Purchase #2	$245.59	10.597%	$271.6152	$271.62	$271.60	$271.60
Purchase #3	$63.37	11.141%	$70.4301	$70.43	$70.45	$70.40
Purchase #4	$61.27	8.352%	$66.3873	$66.39	$66.40	$66.40
Purchase #5	$82.72	11.803%	$92.4834	$92.48	$92.50	$92.50
Purchase #6	$104.58	10.456%	$115.5149	$115.51	$115.50	$115.50
Purchase #7	$54.43	9.822%	$59.7761	$59.78	$59.80	$59.80
7 purchase totals =	$668.22		$739.5417	$739.54	$739.60	$739.50