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	$86.71	4.399%	$90.5244	$90.52	$90.50	$90.50
Purchase #2	$133.71	12.297%	$150.1523	$150.15	$150.15	$150.20
Purchase #3	$27.35	10.848%	$30.3169	$30.32	$30.30	$30.30
Purchase #4	$51.77	4.311%	$54.0018	$54.00	$54.00	$54.00
Purchase #5	$149.34	10.193%	$164.5622	$164.56	$164.55	$164.60
Purchase #6	$201.68	9.510%	$220.8598	$220.86	$220.85	$220.90
Purchase #7	$246.77	5.521%	$260.3942	$260.39	$260.40	$260.40
7 purchase totals =	$897.33		$970.8116	$970.80	$970.75	$970.90