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	$20.80	6.847%	$22.2242	$22.22	$22.20	$22.20
Purchase #2	$39.99	3.202%	$41.2705	$41.27	$41.25	$41.30
Purchase #3	$183.31	9.603%	$200.9133	$200.91	$200.90	$200.90
Purchase #4	$138.98	5.335%	$146.3946	$146.39	$146.40	$146.40
Purchase #5	$85.45	5.387%	$90.0532	$90.05	$90.05	$90.10
Purchase #6	$199.61	4.481%	$208.5545	$208.55	$208.55	$208.60
Purchase #7	$224.40	3.292%	$231.7872	$231.79	$231.80	$231.80
7 purchase totals =	$892.54		$941.1975	$941.18	$941.15	$941.30