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	$111.85	10.657%	$123.7699	$123.77	$123.75	$123.80
Purchase #2	$146.28	11.271%	$162.7672	$162.77	$162.75	$162.80
Purchase #3	$136.90	5.230%	$144.0599	$144.06	$144.05	$144.10
Purchase #4	$5.43	9.756%	$5.9598	$5.96	$5.95	$6.00
Purchase #5	$208.76	6.470%	$222.2668	$222.27	$222.25	$222.30
Purchase #6	$239.58	13.469%	$271.849	$271.85	$271.85	$271.80
Purchase #7	$31.83	9.825%	$34.9573	$34.96	$34.95	$35.00
7 purchase totals =	$880.63		$965.6299	$965.64	$965.55	$965.80