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	$91.35	9.643%	$100.1589	$100.16	$100.15	$100.20
Purchase #2	$48.41	12.106%	$54.2705	$54.27	$54.25	$54.30
Purchase #3	$53.45	4.451%	$55.8291	$55.83	$55.85	$55.80
Purchase #4	$192.95	6.767%	$206.0069	$206.01	$206.00	$206.00
Purchase #5	$249.37	4.796%	$261.3298	$261.33	$261.35	$261.30
Purchase #6	$191.90	11.738%	$214.4252	$214.43	$214.45	$214.40
Purchase #7	$81.43	5.351%	$85.7873	$85.79	$85.80	$85.80
7 purchase totals =	$908.86		$977.8077	$977.82	$977.85	$977.80