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	$46.79	11.837%	$52.3285	$52.33	$52.35	$52.30
Purchase #2	$197.62	13.746%	$224.7848	$224.78	$224.80	$224.80
Purchase #3	$234.49	3.219%	$242.0382	$242.04	$242.05	$242.00
Purchase #4	$162.82	6.111%	$172.7699	$172.77	$172.75	$172.80
Purchase #5	$236.33	13.174%	$267.4641	$267.46	$267.45	$267.50
Purchase #6	$138.63	8.605%	$150.5591	$150.56	$150.55	$150.60
Purchase #7	$127.79	12.320%	$143.5337	$143.53	$143.55	$143.50
7 purchase totals =	$1,144.47		$1,253.4783	$1,253.47	$1,253.50	$1,253.50