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	$38.34	4.132%	$39.9242	$39.92	$39.90	$39.90
Purchase #2	$40.29	12.543%	$45.3436	$45.34	$45.35	$45.30
Purchase #3	$181.50	10.184%	$199.984	$199.98	$200.00	$200.00
Purchase #4	$206.96	10.354%	$228.3886	$228.39	$228.40	$228.40
Purchase #5	$41.61	11.867%	$46.5479	$46.55	$46.55	$46.50
Purchase #6	$137.58	11.622%	$153.5695	$153.57	$153.55	$153.60
Purchase #7	$133.27	9.428%	$145.8347	$145.83	$145.85	$145.80
7 purchase totals =	$779.55		$859.5925	$859.58	$859.60	$859.50