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	$250.63	11.450%	$279.3271	$279.33	$279.35	$279.30
Purchase #2	$177.56	12.573%	$199.8846	$199.88	$199.90	$199.90
Purchase #3	$84.76	3.778%	$87.9622	$87.96	$87.95	$88.00
Purchase #4	$155.71	5.714%	$164.6073	$164.61	$164.60	$164.60
Purchase #5	$30.39	3.862%	$31.5637	$31.56	$31.55	$31.60
Purchase #6	$115.45	6.828%	$123.3329	$123.33	$123.35	$123.30
Purchase #7	$186.68	9.858%	$205.0829	$205.08	$205.10	$205.10
7 purchase totals =	$1,001.18		$1,091.7607	$1,091.75	$1,091.80	$1,091.80