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	$105.52	13.620%	$119.8918	$119.89	$119.90	$119.90
Purchase #2	$8.82	4.330%	$9.2019	$9.20	$9.20	$9.20
Purchase #3	$150.89	4.759%	$158.0709	$158.07	$158.05	$158.10
Purchase #4	$66.46	9.604%	$72.8428	$72.84	$72.85	$72.80
Purchase #5	$50.62	8.115%	$54.7278	$54.73	$54.75	$54.70
Purchase #6	$55.93	13.373%	$63.4095	$63.41	$63.40	$63.40
Purchase #7	$166.37	13.459%	$188.7617	$188.76	$188.75	$188.80
7 purchase totals =	$604.61		$666.9064	$666.90	$666.90	$666.90