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	$92.55	12.647%	$104.2548	$104.25	$104.25	$104.30
Purchase #2	$28.80	5.488%	$30.3805	$30.38	$30.40	$30.40
Purchase #3	$100.56	4.633%	$105.2189	$105.22	$105.20	$105.20
Purchase #4	$148.51	5.103%	$156.0885	$156.09	$156.10	$156.10
Purchase #5	$143.48	12.454%	$161.349	$161.35	$161.35	$161.30
Purchase #6	$93.64	7.381%	$100.5516	$100.55	$100.55	$100.60
Purchase #7	$59.76	6.202%	$63.4663	$63.47	$63.45	$63.50
7 purchase totals =	$667.30		$721.3096	$721.31	$721.30	$721.40