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	$223.81	7.439%	$240.4592	$240.46	$240.45	$240.50
Purchase #2	$137.42	5.835%	$145.4385	$145.44	$145.45	$145.40
Purchase #3	$83.39	8.702%	$90.6466	$90.65	$90.65	$90.60
Purchase #4	$97.87	3.549%	$101.3434	$101.34	$101.35	$101.30
Purchase #5	$68.64	13.540%	$77.9339	$77.93	$77.95	$77.90
Purchase #6	$168.52	7.293%	$180.8102	$180.81	$180.80	$180.80
Purchase #7	$221.70	12.681%	$249.8138	$249.81	$249.80	$249.80
7 purchase totals =	$1,001.35		$1,086.4456	$1,086.44	$1,086.45	$1,086.30