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	$127.70	12.360%	$143.4837	$143.48	$143.50	$143.50
Purchase #2	$76.95	12.457%	$86.5357	$86.54	$86.55	$86.50
Purchase #3	$240.69	4.751%	$252.1252	$252.13	$252.15	$252.10
Purchase #4	$136.38	6.211%	$144.8506	$144.85	$144.85	$144.90
Purchase #5	$21.86	11.805%	$24.4406	$24.44	$24.45	$24.40
Purchase #6	$150.73	9.157%	$164.5323	$164.53	$164.55	$164.50
Purchase #7	$11.51	10.837%	$12.7573	$12.76	$12.75	$12.80
7 purchase totals =	$765.82		$828.7254	$828.73	$828.80	$828.70