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	$86.27	11.737%	$96.3955	$96.40	$96.40	$96.40
Purchase #2	$172.58	9.826%	$189.5377	$189.54	$189.55	$189.50
Purchase #3	$240.98	7.747%	$259.6487	$259.65	$259.65	$259.60
Purchase #4	$212.57	4.677%	$222.5119	$222.51	$222.50	$222.50
Purchase #5	$10.58	5.622%	$11.1748	$11.17	$11.15	$11.20
Purchase #6	$123.49	12.666%	$139.1312	$139.13	$139.15	$139.10
Purchase #7	$112.65	9.404%	$123.2436	$123.24	$123.25	$123.20
7 purchase totals =	$959.12		$1,041.6434	$1,041.64	$1,041.65	$1,041.50