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	$8.45	4.762%	$8.8524	$8.85	$8.85	$8.90
Purchase #2	$161.69	3.307%	$167.0371	$167.04	$167.05	$167.00
Purchase #3	$115.39	13.581%	$131.0611	$131.06	$131.05	$131.10
Purchase #4	$241.40	7.641%	$259.8454	$259.85	$259.85	$259.80
Purchase #5	$119.79	6.716%	$127.8351	$127.84	$127.85	$127.80
Purchase #6	$127.38	11.116%	$141.5396	$141.54	$141.55	$141.50
Purchase #7	$41.40	4.727%	$43.357	$43.36	$43.35	$43.40
7 purchase totals =	$815.50		$879.5277	$879.54	$879.55	$879.50